Designed by Red Sea as a replacement for their Reefer Series Aquariums, the Thin-Mesh Filter Bag helps remove uneaten food, debris, organic waste, or other fine particles. This 225 Micron filter bag is ideal for new set-ups, after heavy maintenance, or whenever there will be a lot of particulate in your aquarium water! This bag is also suitable as a holder for other mechanical or chemical filter media. At 4" in diameter this reusable filter bag is a great addition to existing mechanical filtration in any saltwater or freshwater sump system. Eliminate organic matter which produces ammonia and nitrates, and maintain a healthier aquatic environment with the use of filter bags in your set-up!