This Poly Pad is a dense mechanical filter pad fabricated to remove fine/coarse particulate matter from your aquarium system. This process prevents obstructions in the biological media, thereby diminishing the risk of fish stress and disease. It also helps keep your aquarium water crystal clear! These Filter Pads can be cut and shaped to fit any filtration system, such as: Canister Filters, Hang-On Filters, Trickle Filters, Pond Filters, Wet/Dry Filters, Filter Cartridge Frames, and other mechanical filter applications. Great for both freshwater and marine applications. The pad measures 18" x 10".