American Hydro Systems RR1 Rid O' Rust 2X Concentration Stain Preventer, 1/2 Gallon Bottle, Pack of 4 2X formula is twice as strong as original Rid O' Rust formulas Prevents ugly rust stains and scaling from irrigation well water Use in place of Rid O' Rust Formula 500 and Formula 2000 No.1 Selling rust preventer in the US Keeps your landscaping rust free when used with a Rid O Rust System