Aquarium tank filters come in many different shapes and sizes. They are typically divided into three different categories: biological filters, chemical filters, and mechanically powered filters. Each type, while doing essentially the same job and serving the same purpose, have pros and cons based upon the needs of the owner and the type of fish being kept in the tank. In this article I'll discuss the various aquarium tank filter types and how they work.

A biological aquarium tank filter works by using special types of bacteria that break down harmful chemicals in the tank water. When the fish produce waste, ammonia can build up in the tank and make the fish sick, or even result in the death of some of the fish. A biological aquarium tank filter works by converting that harmful ammonia into less-dangerous forms of nitrites. Typically two types of bacteria are used; one type breaks the ammonia into less-harmful nitrites, then another type breaks down those nitrites even further.

A chemical aquarium tank filter works with the use of activated carbon, which is a highly effective way of reducing chemical buildups and other such pollutants. It does a very good job at reducing the amounts of medications and other treatments that you might have given to the fish or used in the tank for other purposes.

A mechanical aquarium tank filter is the most simple form of filter, in that all it does is remove large particles and coarse pollutants from the tank water. This is, of course, one of the most common types of aquarium tank filters due to its low cost and low complexity. When we're discussing mechanical filters, it's important to note and be aware of the different types that you might come across. Here are a couple of the many variations of mechanical aquarium tank filters:

An under-gravel filter is one of the easiest to maintain because of its simplicity. Simply speaking, an under-gravel aquarium tank filter uses the gravel from the bottom of the tank to filter large particles out of the water, then pumps the cleaned water to the top of the tank. It's a constant cycle of water, but effectively cleans the tank.

An air-powered aquarium tank filter is one of the more effective, though maintenance-heavy types of filters. This variety uses an air pump and filter of some type (this filter can be comprised of many different substances, and can include chemicals or bacteria), and works by screening water through the filter.

Whatever aquarium tank filter you decide to use, make sure it fits your needs and wallet!