ALEGI 4pcs Large Aquarium Sponge Filter with Suction Cups, Check Valves for Breeding Fry Betta Shrimp Fish Tank (Medium for 20-50 Gal 4 Pcs)Brand: ALEGI Color: b Features: Sponge filter provide both mechanical and biological filtration Easy top set up & clean: simply install an airline into the unit and turn on the air pump, simply rinse and squeeze sponge in tank water Using an air hose, connect one end to you air pump and the other end to this filter,and equipped with a check valve on air hose, to prevent water backflow and air pump damage due to power outage. It is a great way to clean