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Filtration is vital for fish to survive in the captive environment of an aquarium. Aquariums are artificial biotopes that rely entirely on the aquarist to survive. Everything that is put into the system and removed is under the direct control of the aquarist. One of the most important tasks for long term success is to control and remove the various toxic wastes that can build up and often kill the inhabitants. Filtration is the function that removes and detoxifies the assorted wastes produced within the ecosystem. Proper filtration, and a rational input of food, is vital to the success for the beginning aquarium, but it takes time to establish appropriate levels of filtration. The novice aquarist should understand what filtration is, and how it can be accomplished. Often the filter is provided in the starter kit, with little explanation of how it performs. Understanding what is actually going on in that media chamber allows an informed choice when adding complimentary filters to strengthen the purification process. This is not a discussion of the actual filtration equipment types available or a discussion of brands and features. That is not in the scope of this article. The actual filter styles will be covered in greater depth in a subsequent discussion. Rather it is an explanation of the types of filtration that an aquarium filter must provide to be an effective component of the aquarium pufification process. I view filtration as divided into three separate functions. - Mechanical Filtration - Biological Filtration - Chemical Filtration Mechanical, biological and chemical processes perform different jobs, although occasionally they will blur the lines of a strict definition. Each identifies and specializes on a different aspect of the pollution problem and uses different methods to perform the job adequately. Mechanical filtration Mechanical Filtration refers to the active removal of solid particulate waste from the aquarium by passing a stream of water through a straining filter material of some sort. The filter material that can be safely used is wide and varied. The important concept is the removal of suspended solids from the tank and then collecting them somewhere that they can be conveniently removed. The media must then be cleaned or exchanged. Mechanical filter media must be maintained on a regular basis. This requires either rinsing to remove trapped dirt or actually replaced. Because the media is a strainer, it will reach a point where it either blocks the stream or fills up and the water flow bypasses it. Most common filter media used for mechanical filters must be removed and replaced after it fills up with the debris it has strained from the passing water flow. Nowadays, the most common mechanical filter is the outside power filter. In its present form, water is drawn from the tank into the input siphon, forced through the impeller chamber and then must pass through the filter media which creates a strainer of various sizes to physically remove the particles from the water flow. Cartridges, which are simply discarded and replaced, are quite popular with many aquarists. I personally prefer a design with maximum filter material blocking the water pathways where the water must pass. Cartridge style filters often sacrifice maximum filter material for ease and convenience. For this reason, the AquaClear power filters are my choice. Their use of the full chamber to house assorted media types makes more efficient use of the available filter area and the water flow through it. Biological Filtration The removal of organically produced nitrogenous toxins dissolved in the water column is the main aim of biological filtration. Generally, there are only two toxins that are eliminated when biological filtration is active. Ammonia and nitrite are produced by the aquarium inhabitants as they go through their lives. Ammonia can be deadly, even in small concentrations. It is produced by almost all life as a by-product of breathing and digestion. In addition, decay processes by bacteria in the system, reduces excess food or other organic wastes to more base components. One of these is the release of ammonia into the water column. Fortunately, nature provides a variety of invisible "friends" for the aquarist. These are able to help control and finally reduce ammonia into less toxic compounds. These are bacteria, often referred to as beneficial bacteria. Some strains use ammonia found in the environment and reduce it to a compound called nitrite. Others take the resulting nitrite and reduce it further to nitrate as they exploit chemical processes to that change as an energy source for their populations. Ammonia is reduced to nitrite by nitrosomonas sp. bacteria, while the resultant nitrite is further reduced to nitrate by nitrobacter sp. bacteria. The true aim of biological filtration is to promote effective removal of ammonia and nitrite through a natural process called the Nitrogen Cycle. Proper biological filtration offers ideal conditions for nitrosomonas and nitrobacter populations to grow and thrive. In the past, most aquariums accomplished this feat by the use of Undergravel Filters with either an air pump or Power Head forcing water to move through the gravel substrate in the aquarium. Nowadays, the Undergravel filter has fallen out of favour, and is normally replaced with a canister style filter and media that is very friendly to promoting powerful bacterial colonies. Most filters have some component of biological filtration in them. All you need for the bacteria is a steady flow of water and a clean hard surface for the lithotrophic bacteria to attach themselves. Many of the media in modern filters will meet this minimal requirement, no matter what their other overall strengths may be. Chemical Filtration Chemical filtration refers to actively changing the characteristics of the water itself. Besides waste particles and dissolved toxins in the water, the actual characteristics of the water, pH, hardness and even dissolved metals, can be altered with assorted chemical and resin substances. Unlike the above two filtration methods, chemical filtration is almost always used in a filter best suited to mechanical filtration. There are a number of filter media that actively change the characteristics of the water filtration as it passes by. Ammonia filtration removers using Zeolite adsorb and chemically neutralize ammonia. Peat, in all its assorted types, softens and acidifies water without necessarily removing any particulate waste. There is a long list of other products which bond heavy metal ions and remove them, change the carbonate content or actively buffer water to a proper pH for a particular species' particular requirements. In addition there are products that remove phosphate and nitrate chemically, usually with a resin of some sort. The only thing these disparate materials have in common is that they actively change the characteristics of the water. How they do it are as varied as the products themselves. Chemical filtration, when actively applied is the field for advanced aquarists, in most cases. But there are many cases where my definition of chemical filtration includes the beginning aquarist as well. Every time new tap water is conditioned, chlorine or chloramine is removed. Depending on the actual product, heavy metals may be neutralized in the process of making the water characteristics safe for fish. Common filtration media, such as carbon also adsorb certain toxins and dyes removing them from the actual water composition. Even the newest aquarist is using all the various types of filtration from the very beginning, whether they realize it or not. So understanding what these types are and exploiting them to the tropical fishes' advantage is vital in success in the first aquarium.
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