MECO 2 in 1 Underwater Air Driven Oxygen Releases Aquarium Fish Tank Pond Biochemical Stone Sponge Corner Filter Supplying the water with much needed oxygen Reduces noise from air pump and consumes lowest wattage Muti-layers, easy to clean and move Various types of installations are possible This filter uses bubbles of air from an external air pump, or an integral water pump to draw water through filter. As water is drawn out through the lift tube or pump, it is replaced by water entering the filter. The top layer of white filter pad provides a mechanical filtration. The black bio-sponge in the 2nd layer and ceramic rings with gravel provides biochemical filtration. They support the colonization of bacteria. The bacteria help to break down harmful waste (ammonia and nitrite).