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By Bob Fenner	A good idea: to remove particulates in-line first

There is a place for everything. For you and I, the third planet from the sun; you can't miss it, the one with the satellite about half it's diameter.

For suspended solids, microbes, mulm, detritus, among other euphemisms for fecal matter, uneaten food... that place is outside your system ASAP. Extraneous material interferes with water clarity, and worse; much of it becomes water soluble, going into solution as more nitrogenous waste, other metabolites, and algal nutrients. Yeah, you know what I'm getting at; pollution.

Mechanical filtration, sieving out and otherwise eliminating particulate matter, living and not, is your first line effort at removing solids. In the previous section, an overview of biological filtration, we broadly introduced these filter modes. Undergravel, box and sponge filters are the tried and trues. Pad three-dimensional media and cartridge types of power filters, DLS (double layer spiral) and other polyester pads in pre- and under-tank filters all attempt to serve the same purpose; principally to screen out solids and secondarily provide as bio-media for beneficial microbes.

Dear Reader, it is up to you to investigate the brands for what is available to you; changes in this field are brisk. Keep in mind a comparison as to efficacy, initial and ongoing, cost and usefulness.

All marine systems should have at least some extra mechanical filtration in addition to biological (and protein skimming). Their purpose may well be redundant, but isn't the cost of a safety-net "back-up" well worth the cost? Yes it is.

Undergravel Mechanical Filtration 

We covered in the last section, and touched on in the way of their media (gravel) in 3) C) Substrates. For physical trapping's sake, the depth, gravel size, screening and flow rate must be matched as previously described. here I'd like to throw my two cents worth in for arranging the flow rate in reverse. Yes there are ways (via powerheads, airlifts, fluid moving pumps in/outside) to pump the system's water up-through the substrate, from underneath to the surface. This is more beneficial than "regular" top-down flow for most marine scenarios. Advantages include ease of cleaning (dirt falls down and out, less compacting, and avoiding messy "rooting" problems with livestock.

Outside Power Filters:

(Due to low flow rates and other inherent maintenance demands we will dismiss air-driven outside filters. Alas, there are only a few of these wonderful devices still on the market. They are still appropriate technology for some types of freshwater systems, but too puny for marine use.)

Small Models:

Small Models: Technology marches on! thank goodness for the progress made in sealed magnetic-drive motors. These units have revolutionized power filters by providing good volumes, with substantial pressures in some cases, of inexpensively driven system water. All this without the dangers of shock/electrocution, except at the plug and wire.

Some of the larger models can accommodate a big system, and there is nothing wrong with utilizing more than one. You are encouraged to purchase or devise a method of "picking up" unfiltered and "returning" the filtered water from as distal a position as possible to ensure optimized circulation.

Inside Power Filters:

Inside Power Filters: are of all the media types as outside; cartridge, sponge, pad, and wet-dry. They have the obvious advantage of not leaking or fighting the effects of gravity to circulate water. Their only real downsides are their obtrusive appearance and possible waste-heat generation. The latter should only be a concern in a very small system.

Many of these units are well made and do a very good job as additional or alternate filter systems. As an additional plus, an internal submersible power filter may be easily moved to establish nutrient cycling, or help out in an emergency, hospital or quarantine tank.

Canister Types:

  Canister Types: are superior to in-tank and hang-on-the-back-types for several reasons. They can be easily remoted, and cleaned with the use of on/off valves with or without quick-disconnects. Canister filters typically have tremendously more filter surface and flow rates as well. But be wary of the claims and performance of any one model/brand.

In particular I caution you to check on the cost of media, and efficiency of flow/volume of water produced per unit energy consumed. There is a huge disparity in what's available in terms of electrical use, pump life, and noise production. Caveat emptor, Let the buyer beware.

The better canister units are silent, consume but a few watts per hour and incorporate large, three-dimensional volumes of media. These require attendance only for cleaning; and this only every few weeks to months. Other cartridge and Diatomaceous Earth types let's sub-classify as pressurized filters.

Pressure Filters: These units can really chew up your electrical bills, so be careful to check their pump/motor rating for energy consumption and to set-up and maintain yours per it's specified range of function. For smaller-large (under a few hundred gallons) pressurized filters are best for periodic (i.e. non-continuous) use; like cleaning, gravel vacuuming. Remember to clean them out when done, so they don't go anaerobic when idle.:

These units can really chew up your electrical bills, so be careful to check their pump/motor rating for energy consumption and to set-up and maintain yours per it's specified range of function. For smaller-large (under a few hundred gallons) pressurized filters are best for periodic (i.e. non-continuous) use; like cleaning, gravel vacuuming. Remember to clean them out when done, so they don't go anaerobic when idle.: These units can really chew up your electrical bills, so be careful to check their pump/motor rating for energy consumption and to set-up and maintain yours per it's specified range of function. For smaller-large (under a few hundred gallons) pressurized filters are best for periodic (i.e. non-continuous) use; like cleaning, gravel vacuuming. Remember to clean them out when done, so they don't go anaerobic when idle.

Humongous systems, and one's with heavy bio-loads (large, big-eater livestock) do well to include a pressurized filter. Some of these use cartridges, sand of different sorts, and other more novel media. Once again, be aware of their costs of operation.

Diatomaceous Earth (D.E.) Filtration

Diatomaceous Earth (D.E.) Filtration: I'll just mention in passing. The ultra-fine single celled (diatom) algal skeleton media used to screen material to less than 1 micron (about 4 hundred thousandths of an inch) makes these units suitable only for periodic "polishing" or transferring of water; in addition to a "conventional" filter system. Existing models require large head pressures, attendant heat and energy, and tend to clog rather quickly. A note here concerning highlights of coming products; this last year at international trade shows I've seen the introduction of new, hybrid D.E./other filters. Keep your eyes open.

Wet-Dry/Trickle Filters:

Should, but do not always include a mechanical filter component; a surprising shortcoming. Quickly and easily removing solids preserves/improves water quality (redox, ph). Real units that do have "pre-filters" of sponge or webbing, polyester sheet or spirals should be easy to get to (many are not) and replace. Best for these are the various "hang-on skimmer boxes" popular in North America.

Mechanical Filter Media:

Wool pads, sponges, sheets, spirals Wool pads, sponges, sheets, spirals are all meant to be chemically unreactive screens, trapping particulates as they pass by and/or through. Nowadays these are all person-made materials that can be cut, shaped, and sewn to any desired shape. Wool pads, sponges, sheets, spirals are all meant to be chemically unreactive screens, trapping particulates as they pass by and/or through. Nowadays these are all person-made materials that can be cut, shaped, and sewn to any desired shape. Wool pads, sponges, sheets, spirals are all meant to be chemically unreactive screens, trapping particulates as they pass by and/or through. Nowadays these are all person-made materials that can be cut, shaped, and sewn to any desired shape.

More frequent rinsing and replacing is the rule, with one final suggestion to "layer" the material to facilitate removing just the dirtiest section; minimizing disruption of your biological filter cultures in the lower media.

Carbon Carbon of different qualities, ion-exchange and other resins are principally intended to be chemical not mechanical media. Take care to treat them as such by using them last in a water flow scheme, after biological and mechanical filtration. At least these materials should be sandwiched between foam/wool pad material to reduce their exposure/gunking up (scientific term). We'll have much more to say about these in the following Section.

Other There are seemingly no end to rings, ceramic beads, turnings, and more incredible adaptations of sewage treatment technology; in part of which includes mechanical filtration. Watch out for mis-leading advertising claims for these. Best to consult with other authentic consumers, at fish stores, hobby organizations, the "net", who can render actual experience comparisons. There are seemingly no end to rings, ceramic beads, turnings, and more incredible adaptations of sewage treatment technology; in part of which includes mechanical filtration. Watch out for mis-leading advertising claims for these. Best to consult with other authentic consumers, at fish stores, hobby organizations, the "net", who can render actual experience comparisons.

References/Further Reading:

Filtration, Central & General

Fenner, R. and Rob Lawracy. 1987. Choosing the right multi-tank system. Pets Supplies Marketing 11/87.

Fenner, R. 1989. Improving your store with central filtration. Pets Supplies Marketing 11/89.

Fenner, R. & Phil Farrell. 1990. An inexpensive aquatic holding facility. FAMA 1/90.Fenner, Bob. 1991. Central filtration systems. FAMA 91.

Fenner, Robert. 1992. Marine filtration: a retailer's view. The Pet Dealer 5/92.

Hovanec, Timothy A. 1995. Central aquarium filtration. AFM 8/95.

Sponge Filters and Materials:

Anderson, Frank G. 1994. Sponges- using and shaping them. FAMA 11/94.

Hayley, Art. 1978. The biological sponge. FAMA 1/78.

Loiselle, Paul V. 1990. Sponge filters- the portable approach to biological filtration. AFM 4/90.

Parker, Nancy. 1975. Polyurethane foam filters. Marine Aquarist 6(1):75.

Undergravel Filtration:

Channen, Robert. 1979. The filter that wears two hats. FAMA 5/79.

Dewey, Don. 1979. How-to: building your own high-efficiency "egg-crate" undergravel filter. FAMA 6/79.

Dow, Steve. 1991. Educate your staff on undergravel filters. The Pet Dealer 12/91.

King, John M. & William E. Kelley. 1973. Efficiency of subgravel filters. Marine Aquarist 4(3):73.

Schiff, Steven J. Aquarium set-up, part II, undergravel filters. FAMA 11/93.

Power Filters:

Potts, Carl. 1992. A tour of the Tunze system. FAMA 8/92.

Schiff, Steven J. 1993. Aquarium set-up; Outside power filters. FAMA 6/93.

Thompson, Richard W. 1990. Power filtration basics: The overflow filter. AFM 11,12/92.

Diatomaceous Earth Filters:

Dewey, Don. 1978. Diatomaceous earth filtration, parts I,II. FAMA 2,3/78.

Ostrow, Marshall E. Diatomaceous earth filtration. TFH 11/79.

Wet-Dry/Trickle Filters:

Delbeek, Charles J. 1990. Reef aquariums: filtration the heart of a reef tank is the filtration system). AFM 2/90.

Thiel, Albert J. 1990. Wet-dry and trickle filters. Pet Dealer 2/90.