1.Retractable fish tank aquarium sponge filter provides both mechanical and bio filtration. 2.Retractable fish tank aquarium sponge filter has air infusion chamber produces minute bubbles which increase the oxygen solubility. 3.Easy to clean: simply take out the 2-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.Culture beneficial bacteria, increase the water level. Don’t wash the sponge in tap water or hot water, or it will reduce the QTY of beneficial bacteria. Only wash in tank water. 6.This fish tank aquarium sponge filter is safe for fish: soft sponge material, tinny holes, won't suck up your fish. 7.This Retractable fish tank aquarium sponge filter is excellent for small size fish like betta, dwarf cichlid, guppy, killifish, goldfish etc., or for hatcheries, maternity tanks, nano tanks and fry tanks, as the filter produces minimal water flow and has almost no way to suck the fish through the filter.