Replacement Cartridge. DuoClear combines the sanitizing effects and water clarity of Nature 2 mineral technology with the convenience of automatic chlorine generation from Clearwater salt technology. The Nature 2 mineral-bed technology uses silver and copper to combat bacteria. The saltwater chlorinator component automatically produces low levels of chlorine, eliminating the need to buy and store chlorine. Together these two technologies create a low-maintenance, low-cost system for pool sanitizing, with water that feels soft and silky.