What is filtration?
In the broadest possible sense, filtration is the act of passing water through some sort of filtration media. The aim is two-fold: to keep the aquarium looking clean for the benefit of the hobbyist, and, more importantly, to provide a suitable environment for the aquarium inhabitants.
There are three types of filtration: Mechanical, chemical and biological.
- Mechanical filtration is simply the physical removal of solids and suspended particles from the water. Mechanical filtration media include filter “wool” (actually fiberglass), poly pads (a fibrous matting), and sponge. If a finer material is used, more and smaller particles will be retained, but the filter media may also become clogged more quickly.
- Chemical filtration is the removal of dissolved compounds by adsorption. The most common chemical filtration media are carbon and zeolite. Various organic impurities, dissolved metals, and chlorine can be removed by chemical filtration.
- Biological filtration is the breakdown of waste products by naturally occurring bacteria. Biological filter media do not break down these waste products themselves but are designed to provide a large surface area and suitable growing conditions for these bacteria. Biological filter media include ceramic or siliceous noodles, plastic bio-balls, sand, and gravel. Any inert material with a large surface area can be a biological filter medium, the larger the surface area, the better.
Which is most important?
Of these types of filtration, biology is the most important in terms of the health of the fish. It is absolutely essential if delicate species and marine fish are to be kept. Mechanical filtration is what keeps the water looking clear, and is also important in that it helps remove solid organic wastes. Most mechanical filters also provide a degree of biological filtration. Chemical filtration is not essential, but helps to keep the water crystal clear and may protect against the build-up of undesirable chemicals in an aquarium. Since most chemical filtration will remove medications it should not be used in quarantine tanks or where fish are being treated for the disease.