Aqueon Coarse Foam Pads provide biological and mechanical filtration for Aqueon QuietFlow 300 and 400 Canister Filters. Coarse pads trap large particles, debris, and solid waste while providing surface area for beneficial bacteria to enhance bio-filtration. Biological and mechanical filtration pads for Aqueon QuietFlow Canister Filters Provides surface area for beneficial bacteria Traps large particles, debris and solid waste Improves overall appearance and water quality Aqueon Filter Media Pads are ideal for both fresh and saltwater use.Small:Fits QuietFlow 200 (#100107312)Large:Fits QuietFlow 300 (#100107313) and QuietFlow 400 (#100107314)