The Elite BioFoam filter provides mechanical and biological filtration for easy aquarium maintenance. Its two foam filters mechanically traps floating debris and biologically cleanses the aquarium water. The air driven system creates suction that allows the foam to capture particles and return purified water to the tank. Harmful wastes are biologically transformed into a relatively harmless substance by aerobic bacteria that can accumulate in the foam. Excellent for use with baby fish. Info from pet Discounters