There are plenty of products available for killing moss. Some fertilizers contain moss killing agents and products containing ferrous sulfate and ferrous ammonium sulfate will work. Algae and moss killing soaps are also available under various brand names.My favorite moss killer is simple Ultra Dawn dish soap mixed with water. It's safe, cheap, and it might already be in your house. A couple of applications of the soapy-water solution will have the moss drying up, turning orange and dying.