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Freshwater Aquarium Filtration: A continued discussion

© Winston Vaughan Schoenfeld

In the previous edtitorial, I listed the three basic types of filtration that aquarium filtration systems use: mechanical, biological, and chemical. In this article, I will discuss some of the freshwater aquarium filtration systems. Freshwater filtration is just as complex as that for saltwater systems. It is the water maintainence that differs. The basic job of a filtration system is to promote the nitrogen cycle of the aquarium, and to remove debris and other particles from the aquarium. For the most part, freshwater aquariums are based on one of two major filtration systems: undergravel filters and box overflow filters (the ones that hang on the back of the aquarium).

Undergravel filters operate by using an uplift tube to draw aquarium water through a filter plate in the bottom of the aquarium. For a diagram of this type of filter, take a look at this page. These filters use biological filtration to keep ammonia and nitrite levels low in the aquarium. The filter plate, and substrate provide the media on which nitrifying bacteria can colonize. Undergravel filters tend to do a good job at maintaining healthy biological cycles in freshwater aquariums. Their main drawback is the effort required in cleaning them. They must be cleaned at least every year, due to the buildup of detritus (debris) above and below the filter plate. This means that one must completely pull up the filter plate during cleaning, which is a real chore. Still, they have proven to be very efficient and reliable.

Box filters are the other main filtering system one finds in freshwater aquarium setups. They consist of a small pump, filter, and carbon insert, all housed in a box which sits on the back of the aquarium. Water is drawn in through a small tube which extends into the aquarium, and flows back into the tank by passing through the filter on to an overhanging lip. These filters provide biological, mechanical, and chemical filtration to the aquarium. The filter acts as the media for colonizing nitrifying bacteria, which provide the biological filtration. It also traps debris in the water, which is the mechanical filtration. The carbon inserts act as the chemical filtration by removing organic material from the aquarium water. The advantage to this type of filtering system is the ease of cleaning and replacing old filters.

There are additional filtration systems that one can find, as well as variations of the above two. When considering which filtering system to buy, it is more important to make sure that the filter is large enough for your aquarium. Most are rated by the number of gallons of water per hour they filter. Beyond this, it is usually a matter of personal preference which will determine the filter you get.

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