Nature2 Express Mineral Cartridge Replacement for Pool Sanitizers For above-ground or in-ground pools up to 25,000 gallons Easy, do-it-yourself installation, everything in one box Superior water quality with lower chlorine requirements Controlled Release Technology (CRT) ensures optimal mineral levels GUARANTEED, Kills bacteria, controls algae, wont stain Replacement mineral cartridge for all Express units Destroys bacteria and controls algae using natural minerals Reduces potential for stinging eyes, skin irritation, and unpleasant odors Will not harm pool equipment or stain pool Helps stabilize pH levels