The under gravel filter is a biological aquarium filter and makes your gravel act as your filtration medium. The Boyu under gravel filter is designed to fit tanks with approximate dimensions of 16" x 11". Due to the three piece plate system, you can use this kit with smaller tanks (having spare plates for future use) or even add a further kit for larger aquariums. It is also suitable for use in almost any shaped tank, due to the versatility of the plates.