A complete system for defending against scale and corrosion. Each Poly Guard System contains one refillable cartridge that contains 24 oz of extended release crystals that will treat 30,000 gallons of water or up to 6 months. The system also includes a clear 10" filter housing with a pressure release button, housing wrench, a filter replacement reminder sticker. Poly Guard Crystals prevent hard water scale, corrosion and iron build-up in water systems, equipment and appliances by forming a protective coating on metal and plastic surfaces. This product is NSF Certified to meet NSF/ANSI Standard 60 for drinking water additives.