4 - Zodiac Nature2 Spa Hot Tub Mineral Purifier Replacement Cartridge W20750. All (4) are Brand New Sealed inside their original boxes. Destroys Algae Bacteria: Effectively kills bacteria and contaminants using silver ions. Family Friendly: Nature2 reduces the potential for red eyes, skin irritations and odors by reducing the need for harsh chemicals. Lasts 4 Months: To continue enjoying benefits of your new spa, replace your Nature2 SPA mineral sanitizer every 4 months. Controlled Release Technology: Nature2 automatically dispenses the right amount of mineral ions into your pool water for continuous sanitizing and healthier pH levels. The Ultimate Spa Experience: Save time and avoid the hassles of traditional chemicals. Nature2 is simple, effective, and more convenient than conventional spa sanitizers.