The Aquatop CAF internal sponge filter is a simple - classic and economical sponge filter for aquariums, the specially developed foam materials of each CAF sponge filter supports the colonization of bacteria - allowing for mechanical and biological filtration. the process breaks down harmful ammonia and nitrite material resulting in a cleaner living environment for your fish. the CAF filter is weighted and uses an airlift system for superior filtration and silent operation.