This is the 200 micron sock capable of removing small particles of debris from your fish tank. Choose from either the 4 inch or 7 inch Ring.Â Filter socks are the most convenient form of mechanical filtration. They remove excess food, detritus, organic waste, dust, and other particulates. Removing these particulates from the water column will reduce the amount of organic matter that produces ammonia and other undesirable substances in the aquarium. Filter socks also help prevent larger objects, such as sand, crabs, snails, etc. from damaging pump motors. Regular filter sock use will lower organic levels and result in CRYSTAL CLEAR WATER!