An aquarium filter is one of the most important pieces of equipment you will add to your aquarium. The filter removes waste and dangerous chemicals from the water. Fish constantly excrete waste as they swim, and this waste can build up in the water and kill the fish. There are three ways that filters clean your water, either biologically, mechanically, or chemically.
Biological filtration removes uses microorganisms to change waste into less dangerous substances. Fish waste turns into ammonia, and the biological filter changes the ammonium into nitrate, which is eventually removed during routine water changes. Biological filtration occurs when the water passes over any surface where the helpful bacteria is growing. Mechanical filtration is the process of removing particles in the water by filtering the water through a filter media, such as a sponge, filter floss, filter pads, or the aquarium gravel. Chemical filtration is done by carbon or other chemicals that remove toxins from the water. Activated carbon makes a great chemical filtration.
A good quality filter will employ all three means of filtration. Here are some common filter types:
- Hanging Filters - Hanging filters hang off the back of the tank and draw aquarium water through a lift tube and returns it through a waterfall. The water is sent through a series of filter media that usually provide all three types of filtration.
- Box Filter - Also sometimes called corner filters, box filters draw the water through filter media that is housed in a plastic box inside the tank, often with an external air pump. The air pump draws the water into the filter, which uses filter floss activated carbon to filter the water.
- Under Gravel Filter - an under gravel filter refers to any filter that uses the gravel as the filter media. The filter is a plastic grate that sits under the gravel, and lift tubes that life the water and deliver air bubbles. The air bubbles are produced through an external air pump. Under gravel filters usually do not have any chemical filtration.
- Sponge Filters - These filters work great for breeder tanks. Water is drawn through a sponge that is mounted inside the tank. An external air pump runs this type of filter. Chemical filtration is available in some models.
- Canister Filter - Canister filters remove water through a sieve, the filter it through a canister. The water is returned to the tank through a spray bar.
- Fluidized Bed Filters - Dirty water from the tank is pushed through a tube off the back of the tank. The water is sent through some heavy granules, which filter the water in the bottom of the tube, and returned to the tank. The filter is powered by a water pump.
- Trickle Filters - Trickle filters remove water through an overflow in an open tower. The water filters through or over the filter media, then is pumped back into the tank through a spray bar.
- Rotating Drub Filter - A rotating drum is a porous cylinder that turns like a paddle wheel as the water runs over it. Rotating drums are often incorporated into hanging filters, and provide ideal biological filtration.
Some filters are a combination of the above types. When choosing an aquarium filter, look for one that uses all four types of filtration, biological, mechanical, and chemical. This will ensure you have the cleanest water possible.