Kobwa(TM) Double Head Air Pump Sponge Filter for Aquarium Tank Size 20 Gallon (Black) with Kobwa's Keyring Material:Plastic; Size:13.5x14x4.5cm/5.31x5.51x1.77inch Sponge filters provide both mechanical and biological filtration Applicable to aquarium below 60L Provides the ideal location for bacterial colonization