There are three main types of tank filters that can be used for turtles; internal filters, hang-on-tank or power filters and canister filters. It is best to avoid using filters that are specifically marketed for turtles because they are generally weaker.
When choosing a filter for a turtle tank, it is important to make sure that the filter is constructed to handle three times the volume of its tank. A tank that contains 60 gallons of water should have a filter that can handle 175 gallons or more. Turtles produce much more waste than fish and therefore need a stronger filter to maintain the cleanliness of their environment. Internal filters are the cheapest filters, however because they are positioned inside of the turtle tank, they tend to take up a lot of space. Furthermore, they generally do not filter out biological impurities. Hang-on-tanks, also known as power filters, are reasonably priced and offer larger filter capacity storage which can house both biological and chemical filtration systems. However, because they hang over the edge of the tank, the water level inside the tank needs to be such that it rises above the lowest portions of the filer. If the water level drops, then the filter may break from running dry. The canister filter is the most recommended filtration system for turtles because it has numerous compartments for chemical and biological filtration systems, and is outfitted with a plastic house that connects the filtration system to the tank at all times without losing valuable space within the tank.