This is the replacement cartridge for the DuoClear Nature2 Salt System. An added feature, only available on the DuoClear, is the Nature2 mineral cartridge. The cartridge contains minerals which are released into the pool to control bacteria and algae growth. This secret weapon allows this system to produce chlorine in much lower amounts and produces unparalleled water clarity, softness and sparkle. With chlorine levels as low as 0.6 ppm, your pool will be much easier to balance and maintain.