Nature 2 DuoClear CartridgeThe Nature 2 DuoClear Cartridge is the best way to maximize sanitizing power in a pool without making the process more difficult. Simply add these cartridges to a Nature 2 Vessel or an existing pool cartridge capable of using DuoClear cartridges, and small amounts of copper and silver are introduced to the pool water for continuous sanitization. This cartridge will fight bacteria and algae for up to 6 months, while helping to maintain healthier pH