Wet & Forget 1 Gallon Outdoor Cleaner. This mold, mildew, and algae stain remover is safe and gentle, non-caustic, non-acidic, and contains no bleach. Simply mix 5:1 with water and apply to sealed outdoor surfaces. It can be used on all roofs, siding, decks, walkways, patios, outdoor furniture, painted surfaces, vinyl, aluminum, and more. It delivers an extended clean up to 1 year or longer. 1 gallon concentrate makes 6 gallons and covers 750 to 2,250 Sq.Ft.