Poly Bio Marine Products APMPF Poly-Bio-Marine Poly Filter Pad for Aquarium, 4 by 8-Inch Highly adsorbent chemical filter media pads quickly and efficiently remove impurities, medications and phosphate from aquarium water Use in conventional power filters, under gravel filters, the chemical filtration compartment of canister filters and wet/dry filters Simply cut to any size or shape to custom fit any aquarium filter Rapidly improves water clarity and actively removes harmful organic and various inorganic waste buildup for several months Measures 8-inch length by 4-inch width