How Aquarium Tank Filters Work

When setting up an aquarium one of the necessary components is a filter, but many people don’t really give the filter much thought. Knowing that you need a filter is the first step, but understanding how aquarium tank filters work and what they actually do will help tremendously in deciding on a filter for your tank.

In short, aquarium filters maintain the water quality in the tank. They do this by removing particles such as food, plant pieces, feces, and other detritus from your water. Filters also remove chemicals and toxins such as ammonia and nitrite from the water. If left to build up these would lead to the death of your fish.

It is important to note that having a good filter doesn’t eliminate the need for regular water changes in your aquarium (roughly 10-20% of the water should be changed every two weeks). Even the best filtration systems cannot remove all water pollution, so the periodic water changes are still necessary. The flip side is true, too, which is that regular water changes by themselves are not enough to keep a tank healthy, and some type of filter must be in place.

A good aquarium filter will provide three types of filtration – mechanical, chemical, and biological. Each element is described below:

Mechanical filtration – This refers to the filtering out of particles in the water, such as the plant scraps, uneaten food, feces, and any other “stuff” that may get stirred up in the tank. This type of filtration is done with a sponge, floss, a coarse pad, or any material that water can pass through, but larger bits and particles cannot. Many filters use an easily replaceable cartridge for the mechanical filtration. When it becomes clogged and water is not flowing freely, the cartridge is simply thrown out and replaced.
Chemical filtration – As the name implies, this involves the removal of chemicals and other (non-particulate) toxins from the water. These include ammonia, nitrite, and other chemicals. This is most commonly done by using activated carbon or charcoal. The carbon absorbs gasses and other dissolved solids, so odors and colors are eliminated from the water. Other resins can be added to the filter that specifically target ammonia removal. This chemical filtration is important because it takes care of things that you can’t see and that if allowed to build up, can cause serious issues for the fish.
Biological filtration – Perhaps the most overlooked but extremely important type of filtration is biological. Many novice aquarium owners do not even know that this is going on, but if it wasn’t occurring their fish would never survive. Biological filtration is accomplished by large amounts of beneficial bacteria in your aquarium filter as well as in the tank itself. The bacteria “eat up”, or metabolize, much of the negative chemicals such as ammonia and nitrite, and convert them into beneficial compounds like nitrate (which feeds live plants). Much of the biological activity occurs in the gravel substrate of the aquarium and indeed this is the reason undergravel filters are the best for biological filtration.

None of the three filtration elements can work independently; all three must be present in a properly maintained aquarium. Having a better understanding of the mechanical, chemical, and biological aspects of filtration will help guide the decision of what type of aquarium tank filter will be best for the style of tank that you wish to maintain.

Andrew Bartlett is an aquarium enthusiast and expert in freshwater fish tank setup, with nearly 30 years of experience.  You can get more information by clicking on www.thefreshwateraquariumguide.com.

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