Pro Poly Guard® slowly releases food grade materials into the water supply, protecting plumbing and water using appliances from corrosion and extending the life of plumbing and appliances by coating the interior walls. This coating of the plumbing also reduces the leaching of copper and lead into drinking water. Poly Guard sequesters hard water (maximum 12 grains per gallon hardness), reducing scale build up, and sequesters low levels of iron (maximum 1 part per million iron), reducing rust staining. The Poly Guard Cartridge will treat approximately 30,000 gallons of water depending on water conditions. Temperature range 40-125º F (4.4-37.8º C). For use on potable water supplies only.