Description: One quart of Formula 500 will treat 125,000 gallons of well water with 1 ppm iron. It is most effective when the pH of the water is 6.0 or higher and hardness measures 15 grains per gallon or less. Formula 500, in a quart container, is at least 2.5 times stronger than an “equivalent” product sold in a gallon container by a national mass merchandiser! It is made for irrigation applications only.