Filter socks stay hidden out of the way in the sump, but they are a boon for clear aquarium water. Micron filter bags provide excellent mechanical filtration, which helps reduce the amount of ammonia-producing organic matter in your aquarium. They also help prevent larger objects such as sand, crabs, and snails from damaging pump motors. Add these Eshopps filter socks effortlessly to any existing sump. Choose from Round or Rectangular Bags; Rectangular Bag offers 2x more filter space than round models, perfect for larger sumps or those wanting to change filter socks less frequently. Plastic ring is 4 inches.