Lees Original Undergravel FilterLees Undergravel Filter is the key to providing a strong biological filtration system. Undergravel filters utilize your tanks gravel substrate as a filtering surface area while providing oxygen to help aerate your aquarium water. Provides biological filtration and aeration to aquarium Includes airline diffusers, carbon cartridges, Discard A Stone and fish saver feature For use in fresh and saltwater aquariums Placed on the bottom surface of the