Strange/mystery film on water surface 10/6/11
Hi crew,
Sorry I've got another one for you - hope you don't mind. Gee you lot are good.
Every morning a 55 gallon tank that I've got set up at the school I work at seems to have some sort of film on the water. Obviously I'm worried about the consequences this has for gas exchange.
I've checked with the cleaners and brokered a compromise where a bleach-based spray (pump not aerosol) they insist on using is only used on the desks. This occurred over a week ago.
Every morning I "wick" the film off (as best I can) with cloth wipes, and afterwards the surface looks like the picture attached - shot from below with killifish saying hi. As can be seen, patches of the film remain after "wicking". The film completely covers the water surface again by the following morning, if not the end of the same day. At this point, there are lots of little bubbles associated with the film.
To check if the bleach-based spray was the culprit, I set up a shallow tray filled with water next to the tank 48 hours ago (soaking a slab of granite in there too). There is no sign of the film as of this afternoon in this tray - this would indicate that the spray is not causing the film?
So I'm stumped. Presumably something in the tank is causing this? It's a new tank that's been set up a month, fish (6x dwarf neon rainbowfish, 1x Golden Wonder Killifish) in for 1.5 weeks and behaving as expected.
Moderately planted with growing Vallisneria, Indian Fern, Java Fern and Java Moss. A few granite rocks, bogwood roots, two terracotta pots and a few river stones (all rinsed/boiled/washed pre-installation as appropriate). 28 deg C, pH 7.2, Ammonia 0 ppm, Nitrite 0 ppm, Nitrate 10 ppm, GH 4 deg.
External canister filter (620 L/hr) handles the water filtering.
Thanks a lot for your help again crew - champions.
Cheers,
Duncan.
<Hello Duncan. If this is what I think it is, it is not uncommon. It's similar to the "protein" that accumulates in protein skimmers in marine aquaria. I think it's a byproduct of biological processes in the tank, and in itself doesn't do any harm. Try increasing agitation of the water at the surface, e.g., with an airstone or a spray bar. If my hunch is correct, you'll see the stuff go away by itself. Cheers, Neale.>

Re: Strange/mystery film on water surface, now BGA 10/6.5/11
Great stuff Neale,
I lifted the spray bar up from about an inch below the water line to level with the water line this morning, much bubbling ensued and the "protein" scum appeared to have cleared by the end of the day. Yay! Bit worried about CO2 drive-off and subsequent plant-growth issues (the floating Indian fern seems to be being beaten around a bit too), but I'm sure it'll be fine.
<Glad this worked. Yes, extra turbulence drives off CO2. But the flip side is that no turbulence encourages precisely the sort of slimy, stinky water you see in ponds. Getting the balance right is the tricky bit!>
I've got another one for you, sorry. I've observed 7 or 8 patches like the picture attached on the gravel substrate of my month-old aquarium. I believe this is blue-green cyanobacteria. Having read Bob's WWM article on the subject, will the extra aeration provided help deal with this? Given the rest of my tank parameters (outlined in previous email) plus my small portions of mini-pellets, wet-frozen blood worms and shelled, squished peas that the fish get fed (all eaten within 1-2 mins), I'm not sure what else to do? This began as a single colony on a Java moss frond 5 days ago, but seems to have spread since then.
Thanks so much team,
Duncan.
<The clue here is where the BGA started -- on the moss. Why? Because moss traps water and reduces current. BGA just LOVES still water conditions.
Almost always, you see it around moss clumps, on the leaves of Vallisneria at the top of the tank, on gravel against the glass, on the feathery roots of floating plants -- all places with low or no water flow. While I know many argue nitrate and phosphate are the major issues, I've got heavily stocked tanks with high nitrate levels and yet no BGA at all. But I also run those tanks at high water turnover rates, 6-10 times the volume of the tank in turnover per hour. My experience is that the more current, the less BGA; whether it physically can't get established or the higher oxygen levels are critical I cannot say. But there it is. Physically remove what's there now, rejig water circulation around the bottom of the tank, and then hope for the best. Cheers, Neale.>
Re: Strange/mystery film on water surface 10/6.5/11
P.S. Sorry, forgot to mention I'll be doing a 20% water change and gravel vacuum tomorrow, my first for this 1 month-old tank. It'll 20% weekly after that.
P.P.S. Going back to an older issue: water pH 7.2-7.4, GH 4. Neale speculated that higher KH may account for the slightly basic pH, in spite of the soft GH. I Measured KH today with a new API liquid kit - KH is 3. So my water is officially soft. So what gives with the pH? Is this a bit weird (Ammonia 0 ppm, Nitrite 0 ppm, Nitrate 10 ppm)? I'm not worried, just interested.
Right, I'm gone now,
Duncan.
<Well, one problem with pH is that it isn't only affected by carbonate hardness, though even a carbonate hardness of 3 degrees KH could result in a slightly alkaline pH like the one you see here, particularly if there's little pushing the pH downwards into the acidic range. So I wouldn't worry too much. Provided it's stable, pH 7.2-7.4 is a great range for a wide variety of fish, including soft water species, which are less bothered by pH than total (general + carbonate) hardness. Cheers, Neale.