A sponge filter uses bubbles of air from an external air pump, or an integral water pump to draw water through the sponge. As water is drawn out through the lift tube or pump, it is replaced by water entering the sponge. The sponge is a mechanical filter and the surface of all the bubbles or pockets in the sponge provide a bed for the bacteria of a biological filter. The bacteria help to break down harmful waste (ammonia and nitrite). Sponge filters provide both mechanical and biological filtration. Most sponge filters are reasonably efficient filters for small volume tanks. These filter are excellent for small size fish like dwarf cichlid, guppy, killifish etc., or for hatcheries, maternity tanks, and fry tanks, as the filter produces minimal current and has almost no way to suck the fish through the filter. Also, the air infusion chamber produces minute bubbles which increase the oxygen solubility. Easy to set up and clean: Simply install an airline into the unit and turn on the air pump, simply rinse and squeeze sponge in tank water. Recommend tank size: Up to 10 gallon each, excellent for small size fish like dwarf cichlid, guppy, killifish etc., or for hatcheries, maternity tanks, and fry tanks, as the filter produces minimal current and has almost no way to suck the fish through the filter. Product dimensions: 2.0 inch D X 4.75 inch H. Package includes: 4 pcs of sponge filters ( air pump and airline tubing not included).