2 ZODIAC NATURE 2 A30 W28165 Aboveground Mineral Cartridge Sanitizers 30K Gallon The Pool Purifier Cartridge For 5.000 30.000 Gallon Pools Replacement mineral cartridge for all Nature2 A vessels Destroys bacteria and controls algae using natural minerals Reduces potential for stinging eyes, skin irritation, and unpleasant odors; helps stabilize pH levels