How Does It Work? 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). What Maintenance Does It Require? The sponge will need to be rinsed every time it becomes dirty, about once every 2 to 4 weeks. It's helpful to reserve the beneficial bacteria by washing the sponge gently with water from the fish tank instead of tap water. Dimension: 2.75"(L) x 3.15"(W) x 7.0"(H)