By Donna M. Recktenwalt
Why filter?
The “why” is simple. Filters clean the water, reduce toxic solubles, exercise the fish, and reduce maintenance time. That’s sufficient reason to use filtration in your aquaria, but even the best systems are only a pale imitation of what occurs in nature. The natural hydrological cycle evaporates water from the seas and lakes and releases it as rain, which filters through soil and rocks, then forms ponds and streams that eventually flow back to the sea. Recreating this cycle, even in small part, benefits the inhabitants of our aquaria.
But what is the best system? That depends on your aquaria and its needs.
In aquaria, filtration follows a pattern similar to that in nature, but on a much smaller scale. Water evaporates from the surface and must be replaced. The remaining water is cleaned by drawing it through filter media where colonizing bacteria help clear it of toxins and residues. Living plants also help utilize waste- and by-products produced by the fish.
This waste, otherwise known as mulm, is a particulate sludge that sinks to the bottom of the tank and the filters. It is not wholly detrimental, since it contains bacteria that aid in the breakdown of nitrite and ammonia, but it is unsightly and contributes to cloudiness. Undergravel filters tend to pull this mulm down into the gravel, where it is further broken down.
The box filter is, perhaps, the most simplified version of the natural hydrological cycle. Mulm is trapped inside the box filter by the foam or polyester floss. Gravel or carbon can also be used in the filters, and the entire structure can easily be removed for cleaning.
Simple air-driven foam filters are ideal for breeding tanks. Fry are not drawn into the filter and the mulm collected on the surface of the foam develops a layer of bacteria and infusoria on which the fry feed.
Power filters are the most useful for cleaning water, with both internal and external designs available. Internal filters are unobtrusive and silent and contain a foam insert that is easy to clean. Carbon can also be added, or ceramic filter material. External power filters are more powerful, producing up to a twice per hour throughput, and require less maintenance. Flow rates vary, depending on the type of filter material used. External filters are often houseed beneath the aquarium, so must lift against the head of water above them. The ideal situation is to have the filter placed beside the aquarium. A downside to power filters is noise. Since the impeller gradually wears the chamber, an annoying rattle can develop with age.
For perfectly clear water, the filter media should filter down to one micron in size, or less. Diatomaceous earth (the silica shells of microscopic animals) is ideal for this. However, diatom filters clog rapidly and require cleaning within an hour or so. They are thus best suited for occasional use as polishing filters. Since they are also expensive, private purchase is often not practical; some clubs have purchased a unit and circulated it among the members.
Most species of fish enjoy water flow and actually swim in the output of the power filters. A stillwater area is recommended, however, and is easily arranged by the use of a few rocks or a flowerpot on its side.
The secret of success with any filtering system is regular cleaning and making certain that the unit is level so water flows properly.
– G.C.K.A. Newsletter, February 1999