The internal power filter is ideal for medium sized aquariums that require more filtration than can be achieved through the use of air driven filters. They are available in a range of sizes to suit tanks up to 4 feet (50 UK gallons) however a number of internal filters can be utilised to accommodate larger aquariums.

Internal power filters are restricted in that they rarely provide any chemical filtration. They usually consist of a cylindrical sponge with a plastic core through which water is forced using an electric pump. The sponge initially only acts mechanically but after a period of time biological bacteria will colonise the sponge and biological filtration will occur.

Internal filters are very quiet during operation and are ideal if space outside the tank is limited. They are extremely reliable and easy to maintain and spray-bars can be attached to most internal power filters to minimise the outlet flow for calmer tanks.