The Fluval Poly/Clearmax Filter cartridge helps control green water and unsightly algae growth by adsorbing and trapping phosphate, nitrite, and nitrate. Provides crystal clear water, a reduction of odours, creates ideal conditions for fish and plants and helps to reduce aquarium maintenance. Replace every 6-8 weeks. To ensure constant presence of beneficial bacteria, replace media cartridges one at a time never together. For freshwater and marine environments.