Aquarium sponge filters are simple, easy to install, and make for an inexpensive form of biological and mechanical filtration. Sponge filters are ideal for aquariums with extremely small fish or fry, as the sponge portion of the filter keeps them from getting sucked up. They make great filters for quarantine tanks, as they won't filter out fish medications. Some sponge filters can be driven by air pumps to increase filter flow and aeration.