These shaped foam pads contain specially structured materials which clean the water they are permeated by the water in a regular fashion and mechanically absorb large and small particles after a short time bacteria gather on the porous special foam which ensure intensive depletion of biological pollutants the set contains 1 x prefilter pad blue 4 x fine filter pad white the blue prefilter pad can be washed and reused several times the white fine filter pad should be changed for a new o