Last year I applied moss killer (liquid concentrate diluted with water from a garden hose) and it worked to control moss in my lawn. However, in applying the spray, I accidentally sprayed some droplets on a wooden Adirondack chair- this created black mottled spots all over the chair that are impossible to remove. I NOW have moss growing on shady spots of my concrete sidewalks thro' the garden...I am TOLD that if I use moss killer on concrete it will STAIN the concrete like it did my chair. Can I add bleach to water and get rid of it that way? What is the best way to get rid of it and keep it from coming back?