Aqua Medic AquaDisc Filter Sponge size 11. Roung filter sponge, manufactured from salt water safe, food grade sponge. The Duo-pack, (2 pcs), contains one fine and one coarse sponge The AquaDisc fits many types of canister filters. The filter sponge is suited for biological and for mechanical filtration. Type 11 - 100 mm (4 inches).