Ortho MossEx Moss, Algae & Lichens Killer, 32-oz. Spray, is a fast-acting formula that kills moss, algae, and lichens within hours. It can be used on lawns, decks, and patios, and won't stain concrete or other surfaces. The active ingredient is 22.11% potassium salt of fatty acids. This product comes in a 32-ounce spray bottle and covers up to 5000 square feet. It is effective for up to 30 days.