1.This sponge filter for aquarium can provide both mechanical and bio filtration. 2.This sponge filter for aquarium has air infusion chamber produces minute bubbles which increase the oxygen solubility. 3.Easy to clean: simply take out the bio sponge, wash it in tank water every month then can reuse. 4.Green color is easy to hide the algae, and more match to your tank landscape. 5.Safe for fish: soft sponge material, tinny holes, won't suck up your fish. 6.Sponge filter for aquarium is excellent for small size fish like betta, dwarf cichlid, guppy, killifish, goldfish etc., or for hatcheries, maternity tanks, nano tanks and fry tanks. 7.Sponge filter for aquarium: we have enough new stock, can ship very fast.