PlenumFAQs

FAQs on Reef Filtration: Plenums 1

Sand sifting animals and plenum 5/6/05 First, like so many people have said before your site is awesome. I really enjoy reading all the advice and gathering information from other people’s questions. I have a couple of questions. My main question has to do with “sand sifting”. I have a 75 gallon tank with a wet/dry, large Excalibur protein skimmer, roughly 45 lbs live rock, 4 inch sand bed (plenum – however, I forgot to add the mesh between layers), Coralife Power Compact Dual Strip Light with 10,000K and Actinic. <The heart of a plenum is the void space under the sand. The screen between the layers functions primarily to protect the plenum. Wet/dries are generally unnecessary with live rock, and often lead to nitrate accumulation. If your nitrates are high, you can remove 25% of the bioballs per week until they are gone and your nitrates should come down.> System has been set up for almost a year. I had a parasite outbreak that wiped out my tank and it has been sitting with my only survivor, a yellow watchman goby, for 2 months to clear. I also have 2 cleaner shrimp, 10 blue leg crabs, 1 scarlet crab, and 5 Nassarius snails. I am looking for something to keep the sand looking nice – right now have some algae going in areas. I have had in the past orange diamond gobies, which I loved, and they did such a good job but could not keep them from going AWOL. I’m also worried about compatibility with the watchman. <Sorry to hear about your parasite troubles. Diamond/sleeper gobies are very difficult to keep alive for long periods of time. Their sifting activity is a search for sand dwelling critters to eat. Even large tanks with very "lively" sand beds rarely have enough of these critters to support these fish. Since many will not accept prepared foods, starvation is common. Also, most of the substrates used in aquaria are very hard on the mouths and gills of these fish.> I was thinking about a sand-sifting star, but was worried about the plenum. Plus, I have seen mixed advice from you on these. Or should I just up my numbers on the crabs and snails? What would be the proper count with my set up? <Snails and crabs aren't really effective sand cleaners and sand sifting stars are predators on the same critters that diamond gobies are. Sand sifting sea cucumbers are great choices, but require fairly fine sand (1mm and smaller). Increased water movement often helps a lot in preventing algae from growing on sand.> I am trying to keep a peaceful community tank. I know that I would like to have 2 clowns, a tang (either yellow or Kole), and thinking about a dwarf angel (either flame or coral beauty). What are your thoughts of this combination and could you recommend maybe 1 or 2 others that might fit in nice. Thank you in advance for the assistance. <This sounds like a nice selection of fish. Other good options include many gobies and blennies, royal grammas and peaceful wrasses. Best regards! AdamC.>

Cold Feet? (Plenum Setup) 4.3.05 Dear all, <Just Ryan with you today! Sprung forward an hour, and feelin' it!> Please help me with some advice on setting up my new tank. I am upgrading from a 70g tank to a 130g FOWLR, he main difference being that I will now have a 70g sump. I am having fun working on it and plumbing it all in without the usual inconvenience of having water in the tank. I had decided to go with a plenum system on the advice of my local retailer, but after spending weeks reading through massive amounts of debate on the net, your site, books etc, I'm just getting more and more confused and worried about it. A main source of problem for me is getting the latest thoughts, as I don't see many new works on the subject. Loads from the 90's, such as my Tullock Natural Reef book, but not so much recently. <Today's SPS craze has pushed demands on water quality through the roof- And thus the technology is born and evolves. Today's use of high quality live rock, precision skimmers and or refugia, and current/wavemakers seem to have great results...But a plenum represents a simple, effective, filtration method in the right application.> Going through all the FAQs is also confusing with different people giving different ideas, and no dates given, though it seemed clear that DSBs were gaining favour. <We have recently started dating the queries. However, I don't think that the effectiveness is lost: They have forced you to visualize the entire process, in more ways than you thought possible!> If I do a plenum system in the sump, with a lower layer of coarser 1-2mm non (less) soluble sand, and an upper level of fine sugar sand, both 2-3 inches deep, with screens between, is this still currently thought of as OK? <Yes> I will be using my skimmer. Is it best to put much live rock / macro algae on the bed and use lighting? Or is it better to go without the plenum and just use a DSB? <I'd skip either in favor of a nice circulation system and well maintained refugia. Although you haven't mentioned what type of bioload/ecosystem you're interesting in keeping, refugia opens all types of doors, without sacrificing nutrient control ability.> Thanks in advance Peter Southampton, England <Good luck! Ryan>

Plenum Riser Function?? Howdy to all! <Jeff> First, thanks for your VAST resource of information. Well I have started 2 new reef tanks for coral farming and propagation. Anthony, I have your book ordered. The tanks are 33 long and 55. Both started with plenums and DSB. Let's use 55 gallon here....(As both tanks have same results and questions) 4-5 inch sand bed. 3/4 reef grade coarse sand, 1/4 sugar fine and live sand, all aragonite (All CaribSea) with a mesh screen 1/2 way down. As per the instructions I followed (at GARF), I installed a riser tube and have a 665 GPH powerhead on it. All seemed very well. ammonia, nitrite, nitrate all zero. Alk 4.0-4.5, Calcium at 400-450. Two Questions: 1) I was told to remove powerhead from riser tube when ammonia and nitrite levels =zero. The tank cycled for 1.5 months (from startup) and all was great. Upon removing powerheads, I found my tanks almost crashed. Ammonia=.50, Nitrite=>1.0, Nitrates at 15-20. I promptly re-installed the powerheads ( after 40% water changes had little to no affect on Ammonia and Nitrite) and overnight, the readings were back to perfect. I thought I wanted a dead water space under the plenum. Yes, No? <Mmmm, well... yes... but what you had, have is not a plenum... is actually a latter day undergravel filter... replete with aerobic microbes... nitrifying bacteria...> 2) I seem to have a pH problem. 8.05-8.10 is where it stays, even adding buffer. I assume the answer has to do with the lack of fresh air, combined with CO2 from keeping all tanks in basement. I thought pH would be no problem, with having over 100 lbs of aragonite substrate. <Mmm, maybe some... but more from your "speeding up" nitrification in the sand bed... this is a reductive process (as in ReDox... reduction/oxidation... aka acid-base chemical reactions... the stealing or giving away of electrons...> Again, thanks in advance as you guys are freakin' fantastic! <Whoa! Take it easy! We're just a bit more experienced pet-fish types like you> BTW, No skimmers running yet, only 2 Sarco's in 55 and 2 colts in 33. I am picking up a phosphate test kit tonight to see if that is my problem. Mike Toole - Detroit, MI <Mike, do turn your skimmer on... Bob Fenner>

- No Plenum, No Problem? - Dear Crew I have had a mixed reef tank for four years now. I regularly take cuttings from my soft corals to the LFS. My stonies however don't seem to be doing so well. I have recently been adding Kalkwasser in conjunction with a calcium reactor as I am getting 40ppm uptake in calcium per day from my massive profusion of coralline covered live rock. This seems to be turning the stonies back to growing levels as the calcium levels are now a constant 440ppm per day (alongside a pH of 8.4). Now my question is this (changing the subject somewhat). Would having a plenum from the start have benefited my system? <Or perhaps just a deep sand bed... there are folks on both sides of this fence as which is "better" but I say they're both useful and worth pursuing.> I have ALWAYS had 10-25ppm nitrate in this system since forever. Could this nitrate level be stunting the coral growth (now I have a hammer coral that is growing nicely since Kalk additions). <I'd say most certainly - nitrates in any concentration above 5ppm have been known to cause problems with invertebrates.> My LFS (who is very well informed) says that a plenum isn't a necessity, other reefers say they are an absolute necessity. <Again, I think you could rework this system and push your substrate depth to about 6 inches. It wouldn't kick in immediately but it would help tackle those nitrates.> I'll be honest it leads me to believe that nitrate isn't that big a problem in a closed system and we worry far too much about it. <There is much research out there that is contrary to that opinion. And more definitively, there is zero nitrate on the reefs of the world; that should be an indication.> Although I can see how a plenum may prevent mulm collection in dead spots, of which I have a lot in my reef system. Just wondered what your thoughts were. <Please read our articles on deep sand beds, I think you'll find them most useful.> An experienced UK reefer who has kept at it. Jim <Cheers, J -- >

A Plenum Pro In The Making! Hello! Thanks for all of the great info! <Our pleasure! We're happy to be here for you! Scott F. here today...> I was reading about DSB’s and everywhere I am seeing stressed over 3 inches to avoid nutrient sinks and the support of efficient denitrification. <That is the prevailing thought...1/2" or less, or 3" or more...> I am using a plenum constructed with lighting grid supported on ? PVC caps with an overall height of approximately 1 inch. Now, my sand bed is on average 4 inches including the sand depth. The sand is a medium grain size. My local pet shop said that the grain size was specifically set up for plenums as the grains allow more water flow to the plenum. Am I creating a nutrient sink? <First- with regards to sand grain size to use in plenums, you are well advised to use 2-4mm size, as this sized grain will help establish dissolved oxygen gradients throughout the bed. Sounds like your dealer is right on. The depth of the sand/plenum is really an absolute...the dimensions have been arrived at through much research by experts in the field, such as Goemans, Jaubert, etc. One to one and a half inches high. You're right on again! Four inches is the recommended sandbed height, too. Everything that you've done is consistent with the established "specs" on plenum system construction. With sound maintenance, overall good husbandry, and excellent observation on your part, you'll be in great shape. I see nothing wrong with your plenum> My Nitrates are 6ppm between weekly water changes, 0 nitrites, 0 ammonia, and Phosphates I am unsure of because I think my test kit is bad. <Do get a new phosphate test kit...A worthwhile expenditure, IMO!> Should I add another 1” of sand? ‘Cause if so my wife is going to strangle me! <Just stick to your plan. No need for an additional inch, IMO. A deeper sandbed over the plenum could actually be a negative, resulting in lower sandbed ReDox levels due to higher levels of nitrogen being stored in the sandbed. You've followed the principles of plenum construction to the letter thus far. stay with it. Good luck! Regards, Scott F.>

- Plenum Questions - Hello! Thanks for all of the great info! I was reading about DSB’s and everywhere I am seeing stressed over 3 inches to avoid nutrient sinks and the support of efficient denitrification. I am using a plenum constructed with lighting grid supported on ? PVC caps with an overall height of approximately 1 inch. Now, my sand bed is on average 4 inches including the sand depth. The sand is a medium grain size. My local pet shop said that the grain size was specifically set up for plenums as the grains allow more water flow to the plenum. Am I creating a nutrient sink? <You're probably on the edge of such things, but I would give it some time. We get a lot of questions from folks who have just set up such systems wondering why they have any nitrates at all, and the truth is it takes months for the plenum and deep sand bed to become fully active and working. They are not instant fixes.> My Nitrates are 6ppm between weekly water changes, 0 nitrites, 0 ammonia, and Phosphates I am unsure of because I think my test kit is bad. Should I add another 1” of sand? ‘Cause if so my wife is going to strangle me! Best wishes, Scott R. <Cheers, J -- >

Anemone Removal I have a 15 gallon high tank which houses a Harlequin Shrimp with his CC star, a few hermit crabs all kinds of snail, a LTA with a Pink Skunk clownfish. I have a HOB filter (which I understand can cause nitrate levels to remain high).<Clean it at least weekly, and it shouldn't be a problem.> The substrate is about 3-4" crushed coral (which I have read is a recipe for disaster). <Not necessarily. With a few detritivores (not too many!) and lots of pods and worms in the CC, it can work well.> I have 15 lbs Bali live rock. I would like to install a plenum to help with nitrate reduction, but am unsure how to safely remove this anemone (if possible at all). He is deeply buried and snaps quickly out of site if touched. My nitrates are only about 15-20 ppm, though this is only because of very frequent water changes. About 5 gallons once or twice a week. I would really like to find a better way. Ideally I'd like to remove the HOB, get more live rock. Install a plenum with 2 layers consisting of crushed coral and live sand. Each layer would be about 2 inches deep. The plenum would be one inch deep and screening would separate the layers. I would also install a small power head. Do you think this would provide ample filtration? That is if I can even remove this anemone. Thanks so much. Corey <I would suggest slowly adding sugar fine sand until the bed is "filled in". This should provide excellent denitrification, and if done a little at a time, the pods and worms will be able to resurface each time. You could choose to either keep or remove the HOB. This way, you won't have to disturb the anemone. Powerheads are very anemone UN-friendly. More live rock should not be necessary unless you desire to have it for aesthetic reasons. Best Regards. AdamC.>

Plenum, sumps setup I have a 55 gallon standard tank with about 80 lbs Bali live rock. This is a glass tank, therefore I installed an overflow about 6 months ago. This overflows to a small refugium (10 ga) located underneath in the stand. <This IS a relative to your main tank, small sump... any chance to double plus size it... or more?> This tank is composed of three compartments. The first being an area containing my protein skimmer, heater, activated carbon. The water then spills over into the next compartment, containing a 4 in live sand bed, with Bali live rock pieces and am growing Caulerpa to assist in nitrate reduction, and also to feed a mandarin in the future. Next the water spills into the next are containing bioballs, and is then pumped back up into the display tank. My refugium is lit 24 hrs a day to prevent it from going sexual. <All sounds good... except my concern should the power or pump go out... do test this... will the water overflow onto your floor?> My nitrates remain about 10-12. Located next to the display tank, I have a 15 ga high tank which has been up and running for about 6 months. My goal is to install a plenum to further help with my nitrate battle. <A good idea> I do 10% water changes to each tack every week or so, and each is lightly stocked. (pair of perculas with carpet anemone, 3 small Chromis plus a handful of small shrimp and crabs in the 55, a pink skunk with LTA, and Harlequin shrimp with his chocolate chip star in the 15) Also I have numerous hermit crabs and snails in all 3 tanks. My question is; what would be the best way to incorporate this 15 ga with plenum into my other system? <Actually, ideally, to mount it at about the same level as your current refugium... to ward against the overflow issue... have water run through it 3-4 volumes per hour... overflow into the ten...> The 15 ga is a glass tank as well and the water level is just about one inch taller than the 55. Ideally I would like the 15ga to overflow into the 55 ga, then down to the refugium, and ultimately back up to the 15 ga. How much would I have to raise my tank in order to do this using a conventional overflow? <Oh... a few inches... depending on desired flow rate should do it. Know that the "transit volume" in the fifteen will now be additional to that of the 55 should power or pump fail... DO run all with the lowest/ten gallon not filled, turn off the pump/s, see where the water rises to below... drain till it's not overflowing, mark the sump/refugium level with a permanent marker, tape... and NOT fill the sump any higher> I'm worried the water being able to drain down the hose and then back up it into the 55 ga without substantially raising it. Any suggestions would be greatly appreciated and a big thank you to your staff which has gotten my tank to where it is today. Corey <Really wish you could add more volume underneath... do look into a container you can tie into the current refugium to take up the excess volume if you can't switch out the ten for something larger. Bob Fenner>

Plenum install to existing setup Hi Robert, <Steven Pro this evening.> Thanks for the extremely helpful site. I have a 55 gallon tank, with fish & coral. For filtering I use LR and a canister filter. I also have a 3-5 inch DSB (crushed coral 3-5mm). <This really is not a DSB, Deep Sand Bed, because you are missing the sand part. What you have is a deep bed of crushed coral and IME/O a recipe for a disaster. Crushed coral has far too large a particle size allowing detritus, dirt, uneaten food, etc. to work its way down into the bed. This will fuel depressed pH and because it will operate largely aerobic, do nothing for denitrification.> Due to high nitrates I change approximately 100% of the water each month. I have read through the FAQ section on plenums. This looks like a good option for reducing nitrates. <As would a true DSB.> I have a few of questions: 1) Should the canister filter keep running during the setup. <Yes, because this may make up a significant portion of your biological filtration. Your crushed coral is working somewhat in this regards and until your new sand is cycled you will need the additional filtration. Better to not change too much at once.> 2) How long will it take to notice a reduction in nitrate <No telling, depends on husbandry, bioload, source water, ...> & will there be any other chemical changes. <Increased buffering, pH stability, and additional calcium> My LFS says there is potential for huge increase in phosphates. <Bogus> 3) I was thinking of installing the plenum in half the tank to see how this goes and then extending to the other half. Are there any problems with doing this? 4) After the plenum is setup should the sand be left alone or sifted? <If inoculated with plenty of critters and your tank does not have too many predators, there should be no need.> Regards, Michael <Have a nice night. -Steven Pro>

Re: Plenum install to existing setup Thanks for your quick reply Steve. Can I just clarify: Do I need to add sand to get anaerobic conditions? <Yes> If I keep an approximate 5 inch bed how much should be sand/how much should be crushed coral? <If you go with the plenum system, there will be two layers, about 50% each.> How fine should the sand be? <Sugar fine for the upper half> Should the sand be above/below the coral? <Above the crushed coral> Can I add and not use a plenum? <If you add a plenum it is being used. It is nothing more than a physical barrier. Perhaps you should search out the works of Dr. Jean Jaubert, the "inventor" of the plenum methodology.> Thanks, Michael <You are welcome. -Steven Pro>

Plenum Bob & Co., <Steven Pro here this evening.> I am thinking about using a simple filter pad (1/2 in thick) along the bottom of my tank as a plenum of sorts. Of course will add aragonite etc. My thoughts are that the pad with its thick maze of plastic media will allow for the anaerobic denitrification sought in a typical plenum while giving surface area for the bacteria to proliferate. Am I off here? <I think that a 1/2" filter pad underneath 4" of sand is quickly going to become a 1/10" filter pad that is no longer porous. If you wish to do a plenum right, I would search for some instructions from Dr. Jaubert. Many plenum systems have had problems and many of those problems can be traced back to an incorrect setup.> Sincerely, Dennis Mao <You are welcome. -Steven Pro>

Re: Tunze skimmers, Nothing To Do With Tunze Skimmers (plenums, denitrification) I always have a lot of concerns which usually end up in a form of a question and it is very nice to find someone to ask them to. This question pertains to plenums under the tank substrate. If the water goes stagnate and air is eventually depleted as this is necessary for anaerobic bacteria to do there thing. It would seem to me to only water to be denitrified is the water in the plenum and very little exchange would take place. <I am going to try to make this very simple, when it is actually a complicated chemical matter. Water would move between these two areas of your tank in an effort to seek equilibrium. Your main body of tank water has a high O2 level while the plenum water has a very low O2 level. But, this is all one body of water that would like to be the same across the board.> Also I have had an idea on a system to reduce nitrates and would be thankful if you would give my your thoughts on it- Using a 55 gal poly drum, place a large foam block in the drum, the foam block would large enough to just about fill the drum, inlet and outlet would be on the top of the drum, inlet water would filtered with a canister filter to prevent solid matter from entering the drum, drum would be kept in a dark room to prevent any plant growth. Idea being center of foam block will be a denitrifier. <Interesting idea but, I think this would become a mess eventually. Have you ever seen a trickle filter at work? No matter how well the water is prefiltered, there is always "dirt" settling at the bottom that must be siphoned out. That "dirt" is mostly dead bacteria that has sloughed off. You would have the same production of dirt in your drum but no way to remove it. FYI, you have this in DSB's too but you have worms, amphipods, copepods, limpets, etc. there to consume it.> Do chemical substances really remove nitrates from the water and are they worth using. <They may work, but not cost effectively.> Thanks again, Rick Luckert <You are welcome. -Steven Pro>

Plenum - to remove or not to remove? I have a 14 month old 40g Eclipse tank. Learning how to keep this in balance has been every bit as interesting and complicated as medical school, which I finished 4 years ago. I certainly find it easier to maintain a room full of premature babies on ventilators than to keep my tank in balance- the more I learn, the more I realize I don't know! <A couple of weeks ago, the premature baby comment would have completely freaked me out. Luckily my wife is now at 39 weeks and doing good.> The burning issue of the moment concerns my "plenum" which is not functioning as such. My tank is overstocked (early ignorance), with 12 goby/blenny type fish (ranging from yellow goby ~1.5cm to flame hawk to 2 alarmingly large Engineer gobies at about 12cm now). I have numerous different polyps (doing well), 50# of healthy live rock, no stony corals. It has a 55w power compact light and a Prizm protein skimmer that produces a couple of oz every 3-4d. I have been battling high nitrates since September. It started acutely with a dead snail and nitrates that leapt from 12.5 to 100 in 1 week, and things have never been quite the same since. In November, I took everything apart and put in a plenum (plastic egg crate, screen, 3" crushed coral topped with 2" aragonite). Initially I did see an effect, with nitrates again in the 5-15 range for a month or so. Then of course my engineer gobies started digging it up. I now have areas where the gravel is 9" deep, covering and killing a powerhead, and areas where the screen is visible. Nitrates have been about 20 for couple of months and just this weekend were 50. I have been changing 10-30% per week using your recommended water change procedures. My phosphates are also high, the worst was 1.0, now around 0.6. I have been using a Polyfilter since mid-January, and Phosguard since Feb. 1, and have started straining my food as you suggest. Through all of this, my polyps look good and I don't have any algae problems (hair algae was a problem in Dec., but GARF reef janitors took care of that completely). I don't have terrible ill effects from the nitrates that I can identify. Still, I am sure things would be happier if I could fix this. It is apparent to me that my plenum is not doing its job in its dug-up state, and in reading it seems I am at risk also for significant hazards related to a malfunctioning plenum. I have been thinking of taking it out, by removing all the tank contents, then vacuuming out the entire substrate, rinsing the bottom, and adding a 1-2" bed of live sand and replacing the tank contents. Should I remove it? If so, is this plan reasonable? What other recommendations do you have with regards to my nitrate problem? (I plan to upgrade to a 130gal with an Ecosystem-type filter perhaps within the next year, and transplant my current menagerie to that). Tracy Creek <Tracy, my recommendation would be to remove the plenum and go with 4+" of fine aragonite sand on the bare bottom of the tank. You are still going to have problems with your fish digging, though. My other recommendations would be to use purified water for water changes, grow some Caulerpa macroalgae in the display, get the larger tank to accommodate all your fish, or find another home for some of your fish. -Steven Pro>

Sand Sifting Star Detrimental to Plenum Setup? I have 40 gallon with a small sump (10 gallon aquarium) that has a 1" plenum and 3" of aragonite sand. Is it possible that the sand sifting star that is in sump could be removing the beneficial bacteria absorbing/eating it)? Or is it doing more help than bad by stirring it up and removing detritus? Are there better creatures for this? (stirring the substrate that is) <Good questions... the Archaster star is doing more good than harm. There are other organisms you could use instead, in addition. Please use the search tool, or marine index to read about "Sand Sifters"... on www.WetWebMedia.com Bob Fenner> Thanks in advance, Dan

Re: How long before plenum becomes effective? Thank you for the reply Anthony. <very welcome, good sir> Just so I have things straight. I do have 3" of sand on top of the actual plenum so a total of 4"). Is this what you are referring to as the DSB? <you actually have a 3" Deep Sand Bed (DSB)... the plenum is another matter, and not so critical to denitrification as sand depth and grain size (sugar fine works best for dentrification> Is that enough? Sounds like you recommend about 5", but does that 5" include the 1" of plenum area? <common legend says (and I agree, having used almost tens of thousands of lbs of aragonite sand in my coral greenhouse with and without plenums <no preference> for years>... that denitrification begins to be compromised when the sand bed wanes under 3". Furthermore, aragonite (fortunately!) has a short half life of less than two years. And so, a tank with 6" of sand only has up to two years before the DSB begins to fail. This is partly why so many people criticize DSB technology and fail early with it... getting misadvised and using too thin of a substrate> I'm just used to people talking about deep sand beds when they aren't using a plenum system. The plenum is 1" thick(1/2" pvc with the 1/2" eggcrate material on top) I put a siphon network in it in case I need to remove water from in the plenum nutrient build-up) <please don't place too much emphasis on the plenum... it's a fine idea, and your design will work if you have screen on top of the eggcrate to prevent the sand from falling through... but nutrient control issues with DSB, again, have more to do with depth (want thicker) and grain size (want finer. never mix grains...old school). Basically, my advice to you would be to add some more sand in the near future, but don't worry too much about how much or how often. If the sand is dissolving and feeding your system properly, you'll have to add sand in the future anyhow. So, at your pace...simply add sand to always be above 3". I mention 5" to most folks because it is deep enough to buy a reasonable amount of time, but not so deep to be detractive visually. In larger systems, deeper is actually better. but in home tanks the point is somewhat moot> Thanks. You guys deserve some kind of civil servant award for all the time you spend answering these questions :) <thank you very kindly for recognizing, my friend <smile>. Best of luck to you. Anthony>

How long before plenum becomes effective? Bob, <Anthony Calfo, in your service> I looked for an answer, but didn't find one on the site. In your experience, how long does the typical plenum take before it becomes effective? I have a 38 gallon tank, with a newly installed 10 gallon sump that has a plenum and a small growing crop of Caulerpa. The sand used for the plenum was fresh special grade aragonite. Nitrates hover between 10 and 15ppm, and phosphates between 0.1 and 0.2ppm. <it is specifically the deep sand bed that becomes "active", and if your sand is deeper than 3" (closer to 5"+) then you can actually see a reduction in nitrates in as little as two weeks (Sprung...and I agree). If your sand is less than three inches...don't even bother to hold your breath <wink>... not going to happen. Need DSB as I suspect you have. Kind regards, Anthony> Thanks for your help in the past. Dan

Plenum Design I wrote you recently about my 220 gallon sand bed reef tank. Your advice was to start over, which I am doing tomorrow, If I want to do a deep bed, would you recommend all fine sand or medium deep with fine on top? <Two grades, levels... as posited on WetWebMedia.com> I was not planning on a plenum this time. Do you recommend a screen between layers? Thanks! Ron

Re: Plenum Design I am sorry, I looked through FAQ and can't find my exact question's answer. I take it you recommend 2 grades of sand. Screen? Thanks. Ron <Yes my friend. Sorry for the trouble. Please see here: http://www.wetwebmedia.com/Plenums.htm and the FAQs beyond. Bob Fenner>

New System Dear Bob, An addition to the previous message! <Please copy/paste, forward previous pertinent information, messages...> Is it a good idea to bypass the Plenum with some of the main tank water, straight into the return chamber? <The plenum? No... unless it is part of a refugium style sump, and you have another parallel sump to bypass it by...> I read somewhere that Plenums don't like too much flow through them. <Think you're referring to something else... Plenums don't have water actually flowing through them. Please read: http://www.wetwebmedia.com/Plenums.htm and the linked files above> For my return pumps I am using 2 Grundfos 15/50 Selectric central heating pumps with Aquaturn conversion kits on them making them safe for saltwater. I got the pumps free from a mate who is a plumber! <These are good products... do keep them free of debris... especially the cooling throughput in the front and back internal (volute) areas... not made to pump particulates> I hope to get it all completed in the next few weeks. I hope you find this letter interesting. When complete I will be more than happy to send you a few photos of the system from sunny England! Eden Maddocks <Sounds smashing. Cheers. Bob Fenner>

Plenum question I just finished reading your article on Wet Web Media.com, and was wondering if your used the same substrate through out the bed will it effect the way it works? <Which article, which "way"?> I wondering because my local fish store sells the CaribSea reef sand and they sell live sand which is from their stock of CaribSea live sand tank, it the same grade of reef sand. So is there a reason for using two different types of grade such as crushed & sand? <For some folks... by and large in small captive systems one grade is best/better> Thanks for any help in this matter. I'm am setting up a 120 gallon tank, I'm stuck on the right way to go about setting the plenum up. thanks again, Tommy <Ah, for a plenum... here it is better to use two grades... Please see: http://www.wetwebmedia.com/Plenums.htm and the FAQs beyond. Bob Fenner>

Moving Substrate to sump, and what kind of Carib-Sea to get? Bob, Thanks for your help recently. <You're welcome> I'm adding a 20 gallon or so sump to my 38 gallon FOWLR. It will have a plenum and macro-algae. I currently have Carib-sea Geomarine crushed coral in my main tank, about 1" deep. I want to change to sand in the main tank. <Good idea> Three things: I want to use the crushed coral from the main tank as the bottom layer in the new plenum for the sump. Is this the right size crushed coral for the bottom layer, and is it o.k. to use the current crushed coral? Or is there a better bottom layer material. <Should be okay... use a plastic screen mesh (like material available for screen door replacement) on top of this layer and finer material (likely coral sand) on top...> I want to change to sand in the display tank. I'm hoping you are familiar with the different Carib-sea kinds of sand. <Yes> What is the best choice for the main tank. It won't be a deep sand bed. The choices are Carib-sea pure Caribbean Aragonite(0.18-1.2mm), Carib-sea Aragamax(0.5-1.02mm), or Carib-sea Special Grade(1-1.7mm) I would like to have a blenny or starfish in the main tank. <Myself... would go with the last (Special Grade)> Of the three Carib-Sea choices above, what is the best choice for the top layer of the plenum? <As stated> Thanks a million, you're an excellent resource, and your book should be arriving on my doorstep today courtesy of UPS. Dan <Be chatting, and taking up your time... pleasurably, my friend. Bob Fenner>

Plenum/Refugium Substrate Bob, Hello! You have a wonderful and informative site which is surely just and extension of your personal endeavors. I have read quite a bit of your information posted and do my best to check out each day's question and answers for odds and ends that aren't necessarily covered in your categorized postings. <Glad we have found each other> I have the following question for you: (in summary) What would you recommend that I use for the substrate in the following setup: 180 gal w/overflow to 50 gal sump Sump contains: Aqua-C EV150, heater, return pump(2500 g/hr pump @ 6.5' of return 3/4" tube), 20 lbs of live rock, and constructing a 16"x28" plenum/refugium(24hr lighted with Caulerpa) <Crushed coral of a "medium" grade... #5, or nominally about an eighth of an inch diameter (for looks, function in this size system)... unless (here come the necessary stipulations, alternatives) you wanted to build a plenum here... or have organisms in mind that require smaller, larger, mixed aggregate...> Mentioned above is a "work in progress" sump upgrade as I currently have a temporary 29 gal (old unused fish tank) supporting the return pump, live rock, and culturing Caulerpa. The temporary skimmer is a CPR Bak pak. I'm currently breaking in the Aqua-C with recycled water from today's water change, and one of the overflow sponges which was heavily soiled.. (I mixed up some really nasty water to break in the skimmer while I finish building the sump). OK, where my question comes... should I use aragonite sand in the plenum/refugium? (wouldn't it dissolve and get clumpy. provides calcium/buffering capacity, but I would have to tamper with it a bit on an annual basis to replenish)... <For this size sump, main tank I'd probably just use live rock in the sump... not make it a plenum... not really large enough for all...> if regular maintenance is required anyway, should I purchase "Miracle Mud" (...do you advocate the use of this? <A possibility... would start off w/o it at this juncture. Though am a fan and friend of Leng Sy, the owner, manager of Eco System> Michael Paletta seems to be a little more than just a "user," more like he is sponsored by "EcoSystem Aquarium." <Do know Mike... and he isn't paid at all by Leng... he is just enthusiastic about the application...> Very little information is available around the web with research/experiences), <Do consult with the various electronic bulletin boards, chat rooms here... there are many vocal folks with experience out there. Ours: http://talk.wetwebfotos.com/ ... look for Des> or should I use non-aragonite sand. <Crushed coral would be best all the way around, for most applications... calcium carbonate based at the very least should be your goal> My plan is 4-5" of sand,.. hmmm, would all 3 be beneficial in specific substrate layers? The sand will be suspended by perforated ?” tubing (as the supports, laying on their sides), plastic egg crate layer (across the tubes, suspended above the plenum floor), and covered by a nylon screen to prevent the sand (and micro-inverts) from passing through. <Oh! Please see: http://wetwebmedia.com/Plenums.htm> BIO load - 2 sm Sailfin tangs, flame angel, 3 damsel fish, 3 small patches of polyps, 100 lbs of 3 yr old live rock. Of course, this is an ever running work in progress, this was a 3 year established 55 gal tank. And since my recent honeymoon(1 month ago) to Maui, HI, there will be plenty more upgrades. We (my wife and I), became SCUBA certified while honeymooning and spent 8 of the 14 days diving and/or snorkeling (diving gets expensive!) <There are ways to reduce costs... as you will learn> in the Hawaiian waters! (Molokini is best!) <A fabulous compressed cinder cone for sure> My wishes to anyone who loves the marine life, please, find the time and the money to go visit the life that you love in their natural habitats. There is so much to learn. <Wish I had written the above! Wait, think I have once or thrice> (And fun to just watch and admire!) (Not only helps your own appreciation, but it also helps when your spouse is able to see for their self what its all about… it’s so much easier when the person who is sharing the bills also appreciates the hobby! …but be warned, it’s only a slight advantage. :) <Amen> Thank you for taking the time to look over all this, and your considerations. -herb <Be chatting my friend. Bob Fenner>

Sandbed question Hello Mr. Fenner, <Hi there> I have been out of the hobby for about 6 years and I am planning on setting up a reef tank in the next couple of months. <Welcome back> I have been reading as much as I can, including some of your articles. There seems to be a big debate on the type of sandbed to use for the best results. The first book I read on sandbeds was Bob Goemans Live Sand Secrets. Mr. Goemans seems to have done a lot of research on the subject and that is why I am leaning towards using a plenum as he describes. <They can be a tremendous boon... done and maintained properly> I have also read that the plenum is a trap for wastes and will eventually ending up causing the tank to fail. <Rare, but does happen> Instead of a plenum you should just put the sand directly on the bottom of the tank. I was wondering what your thoughts were on the subject and what experiences you have had. Thank you for any advice you can give. <Detail to the following can be found in various places on our site (searchable): www.WetWebMedia.com http://wetwebmedia.com/marsubstr.htm http://wetwebmedia.com/Plenums.htm And their associated FAQs files... I am a big fan of the use of purposeful substrates in most all captive marine systems. Would rather place plenums in separate sumps for ease of manipulation... Bob Fenner> Brett Bennett

Re: Reef tank and substrate Ah geez For some reason I never saw the plenum FAQs. You have SO much information on your site :) They answered all of the questions I had asked you. Sorry for the wastage of time Jeff

Re: Reef tank and substrate Yay finally found your book in town. Hard to find. Picking it up pronto :) <You will enjoy and benefit by it I assure you. Bob Fenner>

Plenum in the Sump A couple questions I thought of as I planned my building of a plenum in my Rubbermaid 40G sump. There is very little light if any (even during the day) in my sump because it will be in my stand that is located within an alcove in my home. Is there any reason (or benefit) of having a light on over my plenum/sump? The Caulerpa will be in the filtration compartment turned refugium in the back of my Sea Clear System II tank. <Hmm, yes... if you intend to put some sort of photosynthetic life in the sump/refugium... I would... and it will make it easier to work on...> Do I still need to "churn" the sand in my remotely located plenum? I guess I would do this by hand because it's in the sump? How often? <Not much or often... maybe half of it a month, just the surface... i.e. not the larger grade material beneath the mid-screen...> Are there any benefits of 4" of total substrate as opposed to the 3" (1.5" each) you suggested? <Mmm, yes... if sufficient/proper grade, shape/angularity... more is better... if not and the material channels, clogs, no...> As you know, the Rubbermaid container is not "see through", so I will only have the top view of the plenum as visible. Is there any warning sign of a problem I might miss by not having the side view of the layers? Build up of "black areas" as an example? <IMO/E, not really... smell can be a clue... but measuring, recording the alkalinity, some biomineral like calcium will tell you enough "of the story".> What type of sand should I use on the top layer? Live sand or regular aragonite and wait for it to become live. <The latter in all frankness...> Because the plenum is in my sump and has no live rock above it, there will be not much to make non-live sand turn "live"... is this correct? <Not really... anything live in any part of the system will quickly find its way (if it lives in such settings) to the "sand".> I don't mind spending the extra $$$ if there is a benefit to using the already live stuff. <Not much in this set of circumstances... I would place live rock, some Red and or Green algae/s and lighting here as well though.> Thanks to you as always, Eugene <You're welcome my friend. Bob Fenner>

Plenum in my sump? I almost hesitate to ask you another question, for the fear of being burdensome, but I really appreciate your quick replies and candor. <Okay> To recap, I have a 55 gallon fish only tank with live rock and live sand. The purpose of my next project is natural nitrate reduction and increased water capacity. Should I build a sump or a refugium? <A very good route to go> I only have room for about a 10 or 15 gallon tank inside my stand. My wife will let me do whatever, as long as I don't take up more space than I'm already using! :-) Will a plenum sump or a Caulerpa refugium be "better" for lowering nitrates? <Overall... the Caulerpa if you had to choose... you don't have to... you can/could have both in the same sump...> Does the water "sit" in the plenum sump long enough to get pulled into the plenum for nitrate reduction? Especially in a small 10 gallon sump? <Hmm, yes... enough... Brownian motion, osmosis occurs... with agitation/circulation by whatever pumping mechanism you're using to move the water thither and fro> You mentioned the use of Lights of America florescent lighting. So their standard bulbs' Kelvin rating is sufficient for Caulerpa? <Close enough...> Can you have too much light? <It is possible...> I have their 55W florescent flood lights (http://www.lightsofamerica.com/outdoor.htm model 9027) which gives off a lot of white light, but I'm not sure if it's the right temperature for Caulerpa. I have two, and outside of the California energy crisis, I have no problem with using both if it will benefit the plants. My friend who used to work there thinks that they're around 4,000K - 5,000K. <Some, yes... best to test for yourself...> Whether I create a sump or refugium, here's what I plan to do... please give me a thumbs up if you think it will work... I'm concerned with functionality, cost and of course NO FLOODS. <Okay> - Purchase a CPR overflow to take water out of my main tank. - Hook up that overflow with rubber tubing to siphon? <Yes> water down to my sump/refugium. - Fill the sump/refugium with: - If Sump: all that stuff that makes up a plenum system - If Refugium: small pieces of live rock, no substrate, and a lot of Caulerpa - I assume only about 70% full of water to account for "backflow" <Hmm... do "practice" this by purposely unplugging the recirculation pump... marking the sump at the "highest" full point...> - Lights of America CF lights - A RIO 800 pump (or do I need larger) <S/b big (pressure/flow) enough...> placed inside the sump/refugium with the output connected to rubber hose to push water back up to the main system. Can I put the end of the rubber hose inside the last chamber in my main tank's protein skimmer so that there is only one return tube inside the main tank? <Yes... just make sure it is secured from wiggling free...> I assume because it's a overflow type return tube on the CPR BakPak, it won't overflow the protein skimmer. <Likely not> Is it really this simple? Or am I missing something that will cause my system to flood or be harmful to the aquarium in any way? <This IS about it... Bob Fenner> Thanks as always...

Re: Plenum in my sump? Will a plenum sump or a Caulerpa refugium be "better" for lowering nitrates? <Overall... the Caulerpa if you had to choose... you don't have to... you can/could have both in the same sump...> So you recommend a 15 Gallon Plenum Sump with Caulerpa growing in it? I wasn't planning on partitioning the sump so it would be one main area. Can this still work or should I just go the Caulerpa route? Much obliged.. <I would do the "both" route here... even w/o partitioning the sump in any way. No worries... and you will find nitrates greatly reduced by utilizing both a means of denitrification AND uptake. Bob Fenner>

Some Plenum Questions Bob: I'm thinking about installing a plenum in my 75 G FO system. The tank has only about 45lbs of LR, a DIY wet-dry filter, and an AquaC EV-90 skimmer. Inhabitants are a Naso tang (6"), maroon clown (4"), yellow tang (3"), Paddlefin wrasse (4"), niger trigger (2") and a Huma trigger (3"). Yes, I'm overstocked, and one or more of these inhabitants will be traded in to the LFS when they grow bigger. Nitrates are pretty high despite measures I've taken to reduce them (bottom of wet-dry has submerged Ehfi-Mech and Siporax Beads to host anaerobic bacteria, and a small trash-can within the sump holds Caulerpa and has a light over it). A plenum seems like a reasonably easy and relatively inexpensive way to get additional filtration and nitrate reduction. A few questions if you don't mind..... <Okay, like the explanation thus far> 1) Is it okay to install a plenum into an established tank? <Yes> 2) Is there any particular need for me to remove the wet-dry filter, OR, should I delay the plenum until I've bought enough live rock to take care of biological filtration? (Not sure when THAT would be; tank is heavily stocked with predatory-type fish, and I'm not sure I can rely on live rock alone). In the meantime, the high nitrates are driving me nuts. <You can, will be able to> 3) If I decide to put the plenum in my sump, how do I avoid the problem of massive gravel going up the skimmer pump? <Hmm, it won't... this material is too dense to get sucked up> I'm not crazy about having separate sumps; last time I tried this, there were HUGE sucking sounds from one sump to another. The wife is tolerant of my hobby but did not appreciate the "eternal toilet". <Maybe convert the wet-dry sump into a/the plenum> 4) Given my fish load (triggers and such), am I correct in believing that a DSB alone won't work if it's in the main tank, since the fish would likely eat any detritivores and sand-stirring animals? <Hmm, not a simple yes/no here... both will work, would help> That's why I'm thinking plenum instead of DSB, but maybe you have an opinion on this debate in general or in my particular case. <Mine above> 5) My maroon clown has this annoying habit of sweeping away substrate with his tail, and moving any large pebbles with his mouth. There are huge bare spots on the floor in his territory. Would this kind of behavior cause problems with a plenum or DSB? <She probably thinks you have an annoying habit of sweeping the substrate...> 6) Does Dr. Goemans' plenum scheme in "Live Sand Secrets" work effectively, or is there some other plenum construction plan that I should follow? <Bob G's ideas are very sound here, and in general... his interviews? Bizarre.> Thanks ever so much... <You're welcome, Bob Fenner>

Re: Some Plenum Questions Thanks for your prompt replies -- and for writing "The Conscientious Marine Aquarist. If only they'd initiate a "Fish" category for the Pulitzer Prize . .. Joe <Ahh, you're making my day!> (By the way, where can I find a screen that has a fine enough mesh to keep the oolitic sand from penetrating it? Seems to me I'd have to use a cloth or something similar?) <Yes... I, we just use two, three thicknesses of the inexpensive "fiberglass" screen that we get at "Home Depot" or other such large home improvement outlets... used for screen doors... this works great... Bob Fenner>

Re: Some Plenum Questions Oh - just one follow-up if you don't mind. If I do a plenum, whether in the sump or the main tank, should the upper layer of sand be the fine oolitic stuff or the more coarse aragonite reef sand stuff? <The finer oolithic stuff is better> Most of the pundits out there seem to recommend the latter, but I can get my hands on the former for VERY cheap (thanks to Home Depot and their Southdown Tropical Play sand). Thanks again, Joe <Yes... all the way around. Bob Fenner>

Plenums I currently have a 55 SW setup, fish, liverock, polyps, mushrooms, nothing very difficult. I was wanting to expand and I bought a 110 gallon. Read up on plenum's, started assembly and was just about to install when I ran across A. Thiel's comments. Now I am truly confused/concerned. Do you currently believe the plenum is a good idea? Is it only functional if you have a way to slowly exchange the water under the plenum? I haven't been able to locate much information dated after 1998. I know you are busy but any help/comments would be greatly appreciated. THANKS IN ADVANCE!!! Tim Olsovsky <I think plenums are still worthwhile... given their "proper" maintenance... Much more upside than potential down. But still prefer to remote them in a separate sump... for ease of manipulation. Slowly (or rapidly periodically, as with a valve plumbed to the bottom) moving water in/through the plenum is a good idea IMO. Do seek out and read over my friend, Bob Goemans numerous writings on these devices. He writes about them monthly in the hobby magazine, Freshwater and Marine Aquarium (FAMA). Bob Fenner>

Aquarium-System Hallo Bob . I am from Germany and I find no new article about using a Jaubert-System. I've a working 2000 Liter Tank with Stonecoralls. It's a Berliner-System. But I want to combination these two Systems. My Tank is getting bigger (I make it self every two or tree month). My problem is I don't no how many holes per inch in the Pvc (and how big). And how often must I change (not change but put new after in the downest Place / really bad English) the underground (and is that a problem for the System.). How thick and how big are the Stones small). On the top of the ground must be sand for some animals. Thanks Michael Hannig My English is not good but I work on it >> >> Thank you for writing, and your English is vastly better than my Deutschen! There are many types of Jaubert/Monaco plenum/live sand systems, with variations on items such as: 1) Size, arrangement of the low-oxygen, plenum area underneath. Usually people don't get overly involved in how large or many the holes might be in their bottom support, but quarter inch or so holes ever inch and a half or so will work... Otherwise look around for other chemically inert material to support the upper sand bed. There is a drawing of how this might be done stored on our site: Home Page that you might want to look at. 2) Size, type of the upper sand bed(s)... whether one, two and whether the material is graded. I encourage a larger size under a smaller, separated by a fiberglass screen material (to keep them apart, and keep animals from burrowing through, mixing them) with the upper layer being about 3 mm. in diameter depending on its depth... if smaller, a shallower depth... 3) The material making up the sand beds... should be calcareous and more "round" or spherical in profile... to facilitate even consistent water flow, discourage packing down... Please do write back if any of this is unclear. Bob Fenner

Anaerobic/Jaubert/Plenum/Disasters Bob, been a long time...I've come a long way since we last talked, don't know if you'll remember me. I'm now a technician at Mote and I do research for Marc Weiss Companies and have a small propagation system...I'm asking as many aquarists as I can...Have you ever seen a closed Jaubert system fail as far as alkalinity, pH, and substrate solidification (i.e....Aragonitic concrete?) At Mote, our 2-year old Jaubert tank is failing, exhibiting coralline bleaching and massive bailout. As a result of such events, our new propagation coral lab will be pure Berlin with surge devices, both air piston-driven and bell-siphon (Carlson). Thanks for any observations you can offer Chris >> Know of several such failures anecdotally... can't say/determine how much set-up, maintenance contributes/ed to cause... Bob Fenner Bob Thank you for your observations, and your point on maintenance is well taken...Yet the Monaco aquariums' tanks boast such success (guess the filtration systems aren't a big deal when you exchange ten percent of your bulk water a day with NSW!). <Sometimes only 100% every month... but the point is taken> I have another theory on the reason why the corals in the tank are failing (although over lighting & crashing alkalinity are obvious and deserving scapegoats)...some of my contemporaries share it, some abhor it; All the corals in the failing system were collected from deep (20'+), offshore reefs (Familiar with Looe Key off Ramrod?) <Been there> Offshore reefs, IMO, should be considered completely different microcosm as inshore reefs, whereas inshore reef are immediate recipients of runoff, and their trophically complex food chain is adapted to consume and keep in check algae (i.e. numerous shoals of tang inshore) and zooxanthellae are more keyed into using ambient water concentrations of N for photosystems then using catabolic ammonia from their host's metabolic processes (which is what occurs on offshore reefs). whereas offshore reefs have the luxury of "infinite" dilution, and having the water "stabilized" by N-rich inshore and abyssal ecosystems. <Don't know that I agree with this simple generalization... do you have data to back up this speculation?> I think this has a lot to do with the slow failure of the corals, who were placed in the most unstable ecosystem there is (an aquarium, regardless of size). These corals (at mote) were collected from a deep environment where 65% of the photonic energy from the sun has already been absorbed and they were immediately placed under 4 400watt 6500K halides! we lost 4 out of 15 corals initially and the rest have gone slowly downhill ever since (however with the recent failure of the system, the regression has increased to a blistering pace). Does any of this make sense? sorry for the lengthy explanation thanks again, Chris >> <Need even more lengthy input to render any real help... Could be many factors at play here... even "just" collection, handling trauma prior to your receiving scleractinians... Be all this as it may/will be... I am concerned with so-called pro-anaerobic approaches as the "Jaubert", "Monaco" style filtration... not reasonably safe and effective... thus I stand on a carte-blanche suggestion to folks who would utilize "plenums" to place them outside the main/display system... as in separate sumps for ease of manipulation... and isolation. Bob Fenner>

The endless sandbed debate... Hi Bob, I was wanting to get your opinion on a few things that no one seems to agree on :) Ok, I have written you many times before, but I'll give you a rundown of my system. 9 mo old 55 gallon reef, no sump, 70 lbs live rock, good sized skimmer, no other filtration. I have a couple Euphyllia, mushrooms, polyps, Dendronephthya (yeah, I am bad :P). <If it lives, not so bad...> I have probably way too many fish, although my water quality is always good. (yellow tang, 2 neon gobies, pink spot goby, red lipped blenny, dragonet, three stripe damsel, 2 green Chromis, tomato clown, 2 Firefish, purple tang. cukes, cleaner shrimp, pistol shrimp, flame scallop (that's been doing good for about 5 months now). My sand bed is about 2 inches thick "Carib sea special grade aragonite" with a little bit of courser stuff thrown in. Now, my problem... My tank has gone through a few radical things, the worst being my removal of my undergravel filter about 2 1/2 months ago. before that I was noticing a lot of copepods on the glass and in the sand, but now I don't really see any (although my dragonet seems well fed). <Bingo> I have never seen any worms in my sand, but have seen a few bristleworms on my live rock. Everyone is talking about the value of sandbeds that not only have the bacterial fauna to deal with ammonia, but the macrofauna (??)like worms, mini stars, Mysis shrimp, etc (like Inland Aquatic's detritivore kits) that clean up all the detritus and keep the sand very clean with out any vacuuming or stirring on my part. What I cant get anyone to agree on is whether my live rock will provide these bigger creatures or not. <Indeed they will/do> Some people say no, these life forms don't live on rock, therefore wont come on the rock, others say that live rock makes live sand (or do they just mean a bed of bacteria?). What is your thought on that? <A different mix, but tremendous overlap of all organisms, macro and micro on/in live rock and sand/substrates...> Also, do you think that type of sandbed would be a good thing in my system? I don't want to spend a lot of money ordering a detritivore kit that I may already have naturally in my tank, so any thoughts you have would be appreciated. TIA, <I vastly prefer remoted... sump/refugium type sumps for these adjuncts to improved water quality, than trying to do all in the main/display tank... take a long read through the materials stored, and added on to (like this posting) on our site: Home Page Rachel >> <Bob Fenner>

Shallow plenum I am in the process of "cleaning up" a 55 gallon 2 year old tank following a hair algae outbreak. I have moved all livestock to another tank except for a Pseudochromis (which I can't catch) to another tank. Also remaining are cleaner shrimp, assorted crabs and snails and a leather soft coral. Ammonia and nitrate: 0; nitrate almost undetectable; SG around 1.021. I have a plenum w/only about 1" of marine gravel on the bottom. Don't really know what it is. Also 25-30# live rock. I would like to add some CaribSea aragonite and/or smaller live sand combination to bring the level up to 2.5-3". What would you suggest? Can I add the live sand on top of the existing plenum, or must I take it all out first? <You could add it on top, mix it in... a good idea to do about once every six months after a tank has been up a year> Will such an addition throw off my chemical balance to such a degree that I should first remove all of the remaining critters? <No, likely to throw it in the right directions> If not, would a gradual addition or fast addition make any difference? <Gradual (in two, three divisions) would be better... as would be taking the system apart, putting the new material under the old (between them) with a sheet of fiberglass door screening material> Thanks much. >> You're welcome. Bob Fenner

A bong and a blintz? Bob, I have been reading your book and was wondering, a plenum in a FOWLR, am I better off avoiding that, and instead use more Siporax beads, and possibly a refugium? <IMO, the latter... and if using a plenum, always better remoted in a separate/attached sump/refugium> I have been told that angels don't do well in such a situation (sounds like bs to me, thought I would ask though). <Me too... what is it about Marine Angels...?> With a plenum, what are the chances of deadly hydrogen sulfate pockets and their release? Thanks again tom >> <Some, but slight... if the system is set up "correctly" and maintained (minimally)... with some stirring, vacuuming, no-overfeeding... no inevitable doomsday scenarios. Bob Fenner>

UGF Question, does it matter that I have an undergravel filter plate that is not being used under my gravel. I'd like to use my live rock as my main filtration and so I disconnected my powerheads from it. I was going to take it out when I got my live rock but I was so excited upon receiving it I forgot to, does this need to go? I am afraid gunk will collect down in there with out sufficient bacteria to break it down, or maybe even anaerobic bacteria that will harm my system? Do I need to pull my rock out and take it out, I spent a lot of time creating the perfect scene? Thanks so much I have read nearly everyone of your question answers since June 99 Clifford Ellingson >> Hmm, and wowzah... suspect some folks read more of my stuff than even me! I wouldn't be overly concerned about the undergravel filter placement... some folks in the know, actually do this sort of thing on purpose... The little bit of gunk that will accumulate there is really of no real concern... You'll no doubt have less nitrates... and other metabolite build-up problems... Bob Fenner

One last question do the water areas underneath the plenum need to be connected or can they be divided by the pipes with no detriment? >> They can be divided... though I would leave the pipe ends open and drill some holes through otherwise to allow slow versus no circulation. Bob Fenner

NNR, possibly Bob, First I'd like to say thanks for such a great book, The Conscientious Marine Aquarist I have a 100 gal tank that currently has a crushed coral substrate, about 30lbs of Fla cave rock (limestone) and about the same amount of liverock. filtration consist of a wet/dry with a mag7 for return flow, an RSB skimmer with a mag5 and a couple of power heads in the tank for water movement. It's been set up for about 4 weeks and nitrites are just now starting to drop (0.5mg/l). Eventually I'd like to replace the damsels I currently have with a couple of dwarf angels, maybe a tang and various inverts (hermits, shrimp, snails). I've been reading quite allot on livesand and it's ability to lower nitrates but I have a few of questions. What's the proper way to set up a livesand bed and is there a danger with hydrogen sulfide (sp?) gas buildup? I live near the gulf coast of Fla. Could the sand there be used or is it too fine (it's the white sugar sand)? and finally would livesand even fit into this scenario? >> With some careful construction, a natural nitrate reduction (NNR) system can be almost danger-free... Most involve some variation on the following scheme: from the bottom up. 1) A "dead", low oxygen space called a plenum, trapped under a couple of layers of graded substrate... but first, how to make this space? you can use PVC parts/pipe to support "egg crate/louver" (easy to cut, break with hand tools), covered by fiberglass screen material... that can be panduit/zip-tied down, siliconed on, or just draped over... 2) An inch or two of coarser material... let's say 1/8 inch or so in diameter... covered by more of that screen... 3) and in turn covered by a few (two...) inches of finer calcareous material... graded... maybe... 1/16 inch in average diameter... You can use naturally collected materials... sieve the stuff carefully for metal bits... And you can build, buy, rent screen sieves to grade it... and do freshwater rinse it... and maybe let it air-dry for a few days/weeks... ahead of use... The sand will be "live" any way you arrange it. Bob Fenner

Amount of substrate Bob- If I resituate the NNR in the sump then how much substrate should I put in the main tank, how big of a sump do you recommend and what type of lighting should I use in the sump. Also, should I place some live rock in the sump as well. Do you recommended this because it is more effective or because the amount of substrate in the main tank is ugly to look at? Thanks again. Rob The biggest sump you can fit is the best... And about the same amount of depth... depending on the grades of substrates used for the NNR in the sump... and Yes, I'd place more live rock... and a light over the sump/NNR... and culture Caulerpa there... with the light on 24h/day. and a blend or preferences re resituating the NNR to the sump... both, but more functionally versus aesthetics... It's far easier to manipulate a remoted NNR than thrashing about in your main tank! Bob Fenner Hi Again Bob, I'm not sure I understood your response. Did you mean it's OK to use 2-3 inches of sand without the plenum? If not, what problems would/could I run into down the road without a plenum? Thanks, Tony >> Yes to the three incher... And all sorts of anaerobic nasties problems are possible with poorly built, maintained plenums... algae outbreaks, hydrogen sulfide wipe-outs, a loss of any appreciable calcium... Bob Fenner

Question re plenums Dear Bob, I have had a plenum on a 125 fish and live rock tank for about 6 months. It has worked exceptionally well, lowering nitrates from over 160 to just a trace above zero. I've always had algae growing on the front of the tank below the sand level, even before the plenum. It's usually red or brown, not a major bloom and easily removed. Since adding the plenum, it's a little harder to remove (because the space is tighter) and I can't get all of it. In the past few months, it has been getting darker and I now have what I believe is blue green algae in a small line (about 1/4" top to bottom) along the bottom front edge of the tank. I've added powerheads and redirected flow from my main return (about 1200 gph) toward the front, but it's still there. Phosphates are ever present in the tank and the front gets about 1.5-2 hours of Southern California sunlight (filtered through dark tinting) every day. I suspect the combo of sun, phosphates and the deep sand (about3.5 inches) is the culprit, but I don't know how to get rid of it. Any suggestions? By the way, all the fish (mainly tangs and butterflies) are doing great. I also just added a refugium and a few crops of Caulerpa in the hope of putting some of the phosphates to good use. Do you think, in time the refugium will help with the blue-green or do I have a bigger problem? As always, I look forward to any input you can provide. Thanks for your attention. Dan Pascucci >> Hmm, first off, I'm curious whether this is indeed a type (or more than one) of a blue-green (bacteria) algae... you could scrape some off and take a look/see under a medium power microscope (distinctive... no nuclei, organized plasmids, like chloroplasts...), Secondly, even if so, why the sense of urgency to scrub or remove it... some will not/does not hurt (indeed, the stuff is everywhere).... A few possibilities if you're adamant though... A bit of tape around the edge where the sun won't shine on the band and where you won't be able to see through (the tape)... Redoing the plenum with a gap (a good inch or two) around the plates and supports (draping the screening down to the bottom) where you can scoot the sand aside and get to the area. Bob Fenner

Question re plenums Thanks for the info. That's reassuring. I don't really mind it being there; it's inconspicuous enough. I just have always been under the impression (falsely I guess) that blue-green algae is a bad sign. I guess I'll just keep doing what I'm doing -- removing it when it gets more visible (not a problem lately) and leaving it when it's in small amounts. Thanks for the help. You're so right on the impression... and it's falseness... Some blue green is actually a "good sign"... and often, working to eliminate it (at least appearance) results in far more trouble than just ignoring it. Bob Fenner