What happens when a fish is on the filter?

Many filter types do exist, but they all follow the same format of passing water through a filter medium and sending it back into the tank.

There are three main types of fish tank filters, generally designed for different tank sizes. Gravel filters are the most simple and are more commonly used with the smallest tanks. They work by using an airstone to create a vacuum which sucks water through the gravel bed on the tank floor.

Power filters are usually used in 10-60 gallon tanks. They use a small motor to create a vacuum on the top of the filter, sucking up water from the tank and forcing it through a filter. The clean water then comes back down in a stream. Canister filters are used in medium and large tanks and give users a large selection of filtration mediums. Water is pumped into an external canister and passed through various filters before coming back into the tank.