Decription This is a sponge filter for aquarium which provides both mechanical and biological filtration. Simply install an airline into the unit and provide both aeration and filtration for your fish. Aerobic bacteria colonize the sponge providing a bacterial substance to facilitate the nitrogen cycle. The sponge traps larger waste particles mechanically cleaning the water without trapping baby fish. They are useful for as breeding filter or as secondary filter. Or they can be used as pre-filtration unit by fitting to an external or a filter. Feature - Color: Black - Material: Sponge - Product Dimension: 17.5 x 23.5cm ( Can be extended from 23.5cm to 35.5cm ) - Sponge adopts multi-layer design to acqure large surface so that it doesn't slow down or the flowing current - Simply install an airline into the unit and provide both aeration and filtration for your fish - Aerobic bacteria colonize the sponge providing a bacterial substance to facilitate the nitrogen cycle - Working noiselessly, good permeability, and easy to clean