Filtration is a catchall term for any technique that seeks to maintain appropriate water quality in an aquarium. I define water quality as that set of physical and chemical parameters regarded as typical for the wild aquatic habitat being duplicated. In the case of the tropical coral reefs, very low concentrations of dissolved organic matter and inorganic nutrient ions are the rule, and preventing the accumulation of these pollutants in the aquarium is the primary goal of filtration.

Biochemical activities associated with bacteria living on various substrates constitute a natural pollution-man-agement system that must be encouraged in any successful aquarium. Beneficial bacteria, along with fungi, many types of algae, protozoans, and hundreds of varieties of tiny invertebrates, develop the biological infrastructure of any artificial ecosystem, provided that appropriate conditions are created for their growth and that they are introduced into the system initially Once established, these unseen com-

Reef Filtration

This wet-dry filter configuration — with plastic biomedia, bags of activated carbon, heaters, and skimmer all housed in the sump — is used by many marine aquarists. Simply removing the Bio-Balls and adding live rock and coral sand to the aquarium allows an easy conversion to natural filtration.

munities of organisms make the greatest contribution to water-quality maintenance. The only additional filtration that needs to be supplied to a marine habitat tank is the removal of dissolved organic matter and, perhaps, certain abundant inorganic ions that have biological activity. This material accumulates too rapidly in a closed system for effective removal by purely biological means.

Early techniques for filtration of marine aquariums focused largely on mineralization of organic wastes by means of an undergravel filter, coupled with mechanical and chemical filtration carried out in a separate pump-driven canister or power filter. Natural methods dispense with separate mechanical and chemical filtration stages. Mechanical filtration is defined as the removal of particulate matter from the water. Fastidious mechanical removal depletes the system of natural plankton, important for the survival of many small, encrusting organisms that populate live rock. In a more natural system, particulate filtration is relatively gentle, at most involving foam, floss, or polyester pads placed in the overflow or sump to catch large objects that might cause an obstruction in the plumbing. If these media are cleaned or replaced religiously, they may be beneficial as a way to export nutrients from the system in the form of trapped debris. More often, maintenance is neglected, perhaps because the media are hidden in the overflow, and the trapped debris is broken down by decay bacteria, returning its nutrients to the system. Once a proper balance is achieved, natural systems maintain clear water and accumulate only moderate amounts of debris, without the aid of fine-particle removal. Occasionally, say three times a year, detritus can be stirred into suspension by "blasting" the rocks and aquarium bottom with water from a powerhead or turkey baster. Temporary use of an efficient mechanical filter, such as a canister filter with fine floss, a paper cartridge, or diatomaceous earth (for removal of the finest suspended particles), serves to export nutrients. Leaving such filters in place continuously creates the same problem as leaving dirty filter pads in the overflow: bacteria grow on the trapped waste and return the nutrients to the water, where we do not want them. Some very successful reef aquarists use no mechanical filtration at all on a day-to-day basis, relying on detritus settling in the live sand or sump. Power-filter users are often astonished at the sparkling water quality in such "fil-terless" systems.

Chemical filtration, commonly accomplished by means of activated carbon, is of limited value in the natural marine aquarium. Chemical filtration is the removal of dissolved substances from the water. Besides activated carbon, a wide variety of resins, minerals, and other media have been employed by aquarists in an effort to remove either specific ions like phosphate or a wide range of largely unidentified substances from aquarium water. With the possible exception of activated carbon, there is little evidence to support the need for such media, except in highly specific applications under unusual circumstances. For example, there is an ion-removing resin-bead product that extracts copper ions. Useful, if one has this specific need.

Activated carbon is a mixed blessing. There are many types and grades of activated carbon and much confusion regarding its use. For one thing, some carbons may leach phosphate into the water, contributing to the load of nutrients that one must keep under control. Careful testing of the product you plan to use is the only way to determine if this is going to be a problem. To test, a sample of the product is placed in seawater overnight, and the water is then tested for phosphate. Any detectable amount, using a phosphate test kit with a lower detection limit of 0.05 ppm, is too much. Considering the primary benefit of activated carbon — the removal of yellowing agents that eventually discolor the water — this ongoing testing for phosphates may be too much effort. Yellowing can be eliminated by changing water, and depending upon the dynamics of your system, yellow coloring may only be apparent after a long period without water changes.

The use of activated carbon in reef aquariums is likely to remain a controversial topic for some time. Peter Wilkens, who helped develop and popularize the Berlin method, continues to advocate continual use of pharmaceutical-grade activated carbon to serve as a site for bacterial growth, to remove dissolved organics, and to remove toxins released by captive corals. Wilkens, speaking at the Western Marine Conference in San Francisco in 1996, strongly advocated the use of multiple mesh bags of carbon, with one of the packets being replaced every three to four weeks.

Others, including the noted Norwegian aquarist Alf Jacob Nilsen, have stated a suspicion that continual use of activated carbon can lead to stony coral bleaching if replenishment of trace elements such as iodine is not done on a regular basis (Western Marine Conference, 1995).

Protein Skimming

Of the many possible methods for reducing levels of organic matter in aquarium water, one of the simpler and more convenient is foam fractionation, or protein skimming. In a process analogous to the production of sea foam in surf, injection of air bubbles into the aquarium water creates a meringuelike foam when organic molecules collect at the air-water interfaces of the bubbles. Protein skimmers are designed not only to produce this foam but also to facilitate its collection in a reservoir from which it can be periodically discarded.

Foam fractionation is an important part of the successful maintenance of a marine aquarium. It is the only method available that physically removes organic pollutants from the water. All other techniques simply sequester pollution within filter media, which are then removed and replenished with fresh media. Meanwhile, pollutant molecules may be constantly exchanged between the media and the aquarium water, reducing the overall ef fectiveness of the filtration system. For marine aquariums, foam fractionation is a practical and simple way to control this organic pollution.

There is a bewildering array of skimmer designs and sizes. If in doubt, choose one that is larger than necessary; most reef-keeping experts agree that it is not possible to "overskim" the aquarium. There seems to be no definite answer to the question, "Which skimmer should I buy?" Many authors, including Moe (1989) and Spotte (1992), have discussed skimmer design and selection. Experience has taught me two things about choosing a skimmer: 1) any skimmer is better than none at all, as long as foam is being collected; and 2) use common sense — don't put a tiny skimmer on a giant tank or vice versa. Although any protein skimmer will remove organic matter from the tank, for maximum efficiency, choose one designed for the amount of water your aquarium system will contain.

Skilter Inside Reef Aquariums
Constantly evolving, protein skimmers are available for every level of reef keeping. The Supreme Skilter, left, is a beginner's model; the CPR BakPak, center, is popular for smaller tanks; the ETS, right, is a high-end favorite of advanced hobbyists.

The advantages and disadvantages of the different types of protein skimmers can be summarized as follows: Columnar skimmers that are designed to go inside the tank are simple, foolproof, and relatively inexpensive. They are, however, bulky, and their presence in the tank detracts from the overall natural appearance. External columnar skimmers are more expensive, because they must be made leakproof. In addition, such a skimmer, especially for a large tank, must have a tall column to maximize the contact time between the air bubbles and the water. Thus the skimmer may be too bulky for a particular application. For example, the skimmer may not fit under the aquarium cabinet, out of sight. Many skimmers rely on air diffusers to create a stream of very fine bubbles. These will need periodic replacement.

Further, as the diffusers begin to clog with use, the air supply will require adjustment in order to keep the skimmer op erating properly. Venturi skimmers, on the other hand, do not employ diffusers, but rather use a venturi valve to produce a mix of water and fine bubbles. Therefore, there is nothing to replace, and adjustments may not have to be made as frequently to keep the skimmer working correctly. Some venturi skimmer designs do, however, seem to require constant adjusting. Some old hands prefer the simplicity of replacing reliable limewood airstones every four weeks to fiddling with ill-tempered or ill-designed venturi types. Venturi skimmers are also often designed to create a spinning vortex of water and air inside the skimmer to maximize contact time between the air and water without the necessity of a tall column. Thus a venturi skimmer for a given size tank will always be smaller than a comparable columnar skimmer. The small size means that the venturi skimmer can easily be hidden underneath the tank and will leave more room in the cabinet for other equipment. The primary drawback to venturi skimmers is their relatively greater cost compared to columnar types. Some common complaints about venturi skimmers are that the cheaper models have underpowered pumps and are poor foam producers, some designs are notoriously hard to adjust, and others have air-intake vents that are difficult to access and prone to clogging.

Despite the fact that the basic principle of protein skimming is quite simple, there are a surprising number of skimmer designs on the market. Bearing in mind that no product is perfect, shop for a skimmer carefully. Good workmanship, of course, is a positive sign, but try to see any proposed skimmer in operation before committing to its purchase, especially if it is a costly unit for a large installation. Given the fast-changing nature of skimmer technology, it is difficult or impossible to know what type will be best when you read this book. The wisest approach is to seek the recommendation of someone you trust.

I've had the opportunity to witness many skimmer designs in operation and find that the only common feature of good skimmers seems to be that they succeed in getting lots of fine air bubbles into the water. The foamy mixture of water and air should be so dense that one cannot see through it. Skimmers that yield only large amounts of clear, watery foam are nearly useless and can quickly drain your system of water. The unit should be capable of producing a thick, relatively dry, greenish brown foam, which should be evident in the collection cup when the skimmer has been working on an established aquarium. If the unit meets these criteria and is in use on an aquarium similar to the one you plan, it should work for you.

Aquarium and Fish Care Tactics

Aquarium and Fish Care Tactics

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