Carlisle Trading Co. - Aquarium Filter Socks 5mm Thick, 200 Micron Filtration Extra Thick Filter Bag (5mm) Ensures Your Aquarium Water Will Be Crystal Clear Remove Excess Food, Detritus, Organic Waste, Dust, and Other Particulates to Increase Motor and Fish Lifespan Use-able in Both Fresh and Salt Marine Aquariums Contains 2-Pack of 4" Diameter x 14" Long Felt Filter Socks