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Aquarium Filtration - The 3 Types Explained

There are 3 main types of aquarium filtration. Learn how employing all 3 types will ensure crystal clear water and healthier, happier fish!


If you are new to the aquarium hobby, you may be overwhelmed by the sheer volume of information you need to learn before setting up your first tank. Things like fish compatibility and the nitrogen cycle may seem like foreign concepts that are too difficult to understand, but with just a little reasearch, these concepts are easier to understand than you think. One of the most important things you need to learn about, however, is also relatively easy to understand if you make the effort to do so. Filtration is the key to keeping your aquarium water clean and clear and, as such, it plays a significant role in keeping your fish healthy. Filtration is actually a relatively simple concept to understand, and once you grasp the basics, you will be equipped to select the right filter for your particular aquarium.

Mechanical Filtration

filter xs 6368101The first type of aquarium filtration is also the most basic – mechanical filtration. This type of filtration simply involves the removal of solid waste from the water in your aquarium. In the aquarium, solid waste may take the form of uneaten fish food, feces and plant matter. Different types of aquarium filters function in different ways but, in most cases, mechanical filtration is accomplished through the use of an intake valve or tube which sucks up the water in the aquarium and filters it through a sponge, or other media, before spitting it back out into the tank. As the water passes through the sponge, solid waste particles become trapped, leaving the water that is returned to the tank that much cleaner. Over time, waste particles will clog the sponge so it must be replaced, or cleaned, at least once a month to ensure adequate filtration.

Chemical Filtration

Coal 2151884While some type of sponge is generally sufficient to remove solid waste particles from aquarium water, it cannot remove dissolved wastes and organic pollutants. Some of the pollutants chemical filtration helps to remove include organic acids, proteins, hormones, metabolic waste and organic compounds. In order to remove these substances, many aquarium filters include some type of chemical filter media like activated carbon. As water is taken up into the filter it passes through the sponge, which absorbs solid waste particles, and the filter media which absorbs the organic pollutants. Chemical filtration also helps to remove a variety of toxins including ammonia and nitrate, though a third type of filtration is necessary to completely remove these toxins from tank water.

Biological Filtration

Bacteria 25517966The third type of aquarium filtration, biological filtration, is often overlooked by novice aquarists but it is just as important as the other two types. Rather than involving the removal and physical filtration of aquarium water, biological filtration simply refers to the establishment and maintenance of a colony of nitrifying bacteria in your tank. As debris builds up in the bottom of your aquarium it will begin to break down and produce ammonia, a toxin harmful to fish. The beneficial bacteria take that ammonia and convert it into nitrites and then into nitrates which are not harmful in small doses. This process, called the nitrogen cycle, is imperative to the healthy maintenance of your aquarium and it is carried out by two types of bacteria – nitrosomonas and nitrobacter.

Some aquarium filters, such as hang on the back filters, now include a sort of wheel which spins as filtered water is returned to the tank. This wheel serves no other function but to provide beneficial bacteria with a place to grow. If your aquarium filter does not have a biological filtration component there are other places in your tank where the bacteria are likely to grow. Beneficial bacteria inhabit the substrate in your tank as well as large in-tank surfaces such as rocks and other aquarium décor. If this is the only form of biological filtration you have going in your tank, be careful not to clean your substrate and tank decorations all at once or you may kill off your entire colony of beneficial bacteria at once.

Tips for Selecting an Aquarium Filter

aquarium xs 18565953When it comes time to choose the main filter for your aquarium, it is wise to select one that incorporates all three types of filtration. If you are simply looking for a supplemental filter for your tank or for a filter for a hospital or nursery tank, however, a filter that provides only mechanical filtration may be sufficient. Chemical filtration is not recommended for hospital tanks because the filter media may filter out any treatment you administer. In a breeding or nursery tank, fry are unlikely to produce a significant amount of waste necessitating the use of anything more than mechanical filtration.

Though there are only three types of aquarium filtration, there are many types of aquarium filters on the market. These filters range from basic sponge filters to complex sump systems so it is easy to become confused when trying to make a decision. If you are unsure what type of filter is best suited to your tank, do some research and read consumer reviews to get a feel for the different types and brands of filters available. If you prefer, you may also speak to the professionals at your local pet store for recommendations. Once you have chosen the type of filter you want to use all you have to do is purchase one the correct size for your particular tank. After you have set up the filter, you will have relatively little as far as filter maintenance is concerned. Simply replace the filter media once a month and this, along with regular water changes, will help to keep your aquarium clean and clear.

By employing all three types of aquarium filtration, your fish will enjoy much cleaner water and more stable water parameters, and you'll enjoy the time saved for aquarium maintenance and have happier, healthier fish.

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