Filtration Types

Introduction

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 jobs for success is to control and remove toxic wastes that can build up and kill the inhabitants. Filtration is the function that removes and detoxifies the assorted wastes produced within the ecosystem.
I view filtration as divided into three separate functions. Mechanical, biological and chemical filtration perform different jobs, although occasionally they will blur. Each identifies a different aspect of the problem and uses differant 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 flow through a straining filter material of some sort. The filter material used is wide and varied, but the important concept is the removal of solids from the tank and depositing them somewhere that they can be removed and exchanged. Mechanical filter medias must maintained on a regular basis. Because the media is a strainer, it will reach a point where it either blocks or fills up. Most filter media used in mechanical filters must be replaced after it fills up with 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 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 more filter material blocking the water pathways than these units can offer. 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 that are dissolved right in the water water column is the main aim of biological filtration. Ammonia and nitrite are produced by the aquarium inhabitants as they go through their lives. Ammonia is deadly, even in small concentrations, and it is produced by almost all life as a by-product of breathing and digestion. In addition, decay processes occuring on excess food or other organic wastes also release ammonia into the water column.
    Fortunately, nature provides two invisible friends for the aquarist that are able to help control and reduce ammonia to less toxic compounds. These are bacteria, often referred to as beneficial bacteria which use ammonia and its direct by-product nitrite 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 the natural process called the Nitrogen Cycle. Proper biological filtration offers ideal conditions for nitrosomonas and nitrobacter populations to grow and thrive. In most common aquariums this is accomplished by the use of Undergravel Filters and either an air pump or Power Head forcing water to move through the gravel substrate in the aquarium.

    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 characterisics 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 as it passes by. Ammonia 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 the species you want to keep. In addition there are products that remove phosphate and nitrate chemically. 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.

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