Fluval Clean & Clear is a new filter media for the operation in the internal filters of the Fluval U Series or any other aquarium filter. Fluval Clean & Clear contains a special high performance resin to reduce phosphate and nitrate for a cleaner Aquarium water and healthier fish. Fluval Clean & Clear helps to reduce algae problems and increases cleaning intervals. Add the filter insert to the central Fluval U cartridge alongside the Biomax. The medium is acive for approx. one month and should be replaced after this period.Fluval Clean & Clear Filter Insert U Series+ helps keep aquarium water beautifully clear+ extends time between water changes