One gallon of Rid O' Rust Liquid Rust Stain Remover will treat approximately 400 square feet. Safe for use on concrete, vinyl, asphalt, brick, stone, wood, and virtually any exterior surface. Safe for plants when used as directed. Simply spray, watch stain disappear and rinse. It's that easy. Use Rid O' Rust RR1 to prevent UGLY rust stains caused by irrigation well water. Apply the formula through American Hydro Systems injection or siphoning system to prevent sprinkler stains from well water forever. RR1 is used for water with a pH of 6 or greater and any hardness level. 1/2 gallon (64 Oz. ) of RR1 will treat 125, 000 gallons of water with 1 ppm iron. Keep the rust and iron staining off all your outdoor surfaces using Rid O' Rust preventers.