Stain and Scale controls problems caused by high amounts of metals, and it inhibits the formation of rusty brown, black, or green water and cloudy precipitates in hot tub water. Most colored water problems and stains are due to the presence of metallic impurities, such as iron, copper and magnesium salts. These impurities may be present in the water used to fill the hot tub spa, or they may develop over time from the corrosive action of acidic water (low pH) on metal pipes and plumbing equipment. Upon initially filling your hot tub with water, simply add a small amount of Stain and Scale and use each week as a preventative measure. This product is also known as Metal Gon.