Ecoolbuy Biochemical Filter Cotton for Aquarium Fish Tank 90x30x2cm Dense hole clearance and softness, and through expert analysis is the best to cultivate good hotbed of nitrifying bacteria. On the biochemical cotton waste and feed residue, improve water quality filter clean. Best effect, reduce the fish mortality. Cleaned once a month, no blocking, no deformation, can be reused after cleaning. Material: Sponge Size: Approx. 90x30x2cm (L*W*H)