Nature2® W28165 A30 Single Cartridge, 30K gals, 4/Case is the perfect replacement for your alternative sanitizer system. Equipped with three female ports, this cartridge fits only Limited Nature2® vessels. The silver ions in this cartridge are great for controlling pool algae and eliminating bacteria from your water. This Nature2® Replacement Cartridge is replaced once every six months to maintain clean, clear, and healthy water. Nature2® mineral sanitizing systems are easy to use and eco-friendly. By using this sanitation system, you may be able to reduce bromine and chlorine usage by up to 50%. Eliminate the feel, smell and other side-effects of harsh chemicals!