Aquarium Internal Filters

This type of filter utilises an electrically powered centrifugal pump to draw water through the filter material, which is normally a sponge. They may have additional chambers for absorption media or additional mechanical / biological media. They generally create a more powerful circulation than air-powered filters. 

Internal filters are ideal for aquariums in the 2ft - 4ft size range, and are useful in combination with external canister filters for large aquariums. They also provide useful extra mechanical filtration when used in conjunction with undergravel filtration.