Micron filter bags provide excellent mechanical filtration, which helps reduce the amount of ammonia-producing organic matter in your aquarium by trapping debris which also helps prevent large and small object like sand and coral from damaging aquarium equipment. Solid construction and heavy duty stitching make these socks strong and durable so they can be cleaned and reused numerous times. You will receive twelve 4 inch filter socks. Bring clarity to your aquarium with our professional grade micron filtration sock. Micron filter socks are an essential part to keeping aquarium water clear and clean.