Dr. marine 2PC Filter Sock 4" X 12.2" 200 micron Polyester Aquarium Two suture Felt Filter Bags, 4 Inch Ring by 12.2 Inch Long Filter socks are the best form of mechanical filtration. This is an essential part for wet/dry filter systems, sumps, and diy filters. Removes excess food, detritus, organic wastes, and other particulates to lower ammonia levels and other undesirable substances. Used as mechanical filtration for any sumps and diy filters Quality: 2 Pieces