The Aqua One 5s Sponge pad set is a rinsable filter foam pack for use in the AquaStyle(AR) 980 aquarium . The foam layer goes between the Carbon C cartridge and the bottom layer of BioNoodles. It traps larger debris and cultures helpful aerobic filtration bacteria. A pack of three sections is supplied and the sponge sheets should be removed and rinsed in a little aquarium water (not tap water) when blocked with fish waste and debris. This will usually be every four to six weeks. After several months the foam cell structure begins to break down and the sponge pads should be replaced.