1.With multi-layer corner sponge filters: this corner sponge filter combines physical and biochemical filtration for your fish and increases the oxygen solubility. The top layer of white filter pad serves a mechanical filtration, and the black bio-sponge and ceramic rings work as a biochemical filtration and support colonization of beneficial bacteria. 2.Quiet filtering system: Especially good for breeding small fish. Efficiently remove toxic waste and maintain clean water for your fish. Each unit requires an air pump and airline tubing to operate together (sold separately, not included). 3.Easy clean and maintain: just take out the sponge and rinse well when it becomes dirty. It's complete set and includes all the filter components - gravel, ceramic, sponge, etc. 4.This corner sponge filter is excellent for small size fish like dwarf cichlid, guppy, killifish, shrimp etc. Efficiently remove toxic waste and maintain clean water for your fish. Each unit requires an air pump and airline tubing to operate together.