Zodiac Nature2 Above-Ground Pool A Sanitizer Replacement CartridgeNature2 A brings all the sanitizing benefits of mineral technology to your above-ground pool. Using patented Nature2 technology, this sanitizer cuts chlorine requirements, reducing the potential for skin and eye irritation, and unpleasant odors. With Controlled Release Technology, natural water conditioning capabilities and a stabilizing affect on the pH balance, the Nature2 A gives you more time to enjoy the water. Replacement Cartridge fits the Nature2 Model A for above-ground swimming pools. Cartridges should be changed every 6 months to ensure optimal performance.