Sponge filter provides both mechanical and biological filtration. Aerobic bacteria colonize the sponge, providing a bacterial substrate to facilitate the nitrogen cycle. In addition, the sponge traps larger waste particles, mechanically cleaning the water. It is an important instrument to successfully keep aquatic fish for respiration process. What Maintenance Does It Require? The sponge will need to be rinsed every time it becomes dirty, about once every 2 to 4 weeks. It's helpful to reserve the beneficial bacteria by washing the sponge gently with water from the fish tank instead of tap water. Features: Supply the water with much needed oxygen Reduce noise from air pump and consume lowest wattage Multi-layer media, easy to move and clean Easy-to use biological filter for tropical aquarium fish Description: Color: Blue Material: ABS Plastic Dimension: 8cm*8cm*8.5cm / 3.15 inch*3.15 inch* 3.34 inch Compatible for small aquariums, need to use with an air pump (Not Included) With elegant appearance, economical and functional Package Includes: 1* Blue Fish Tank Filter