As Soon as a roofing manufacturer lists a green product as safe to put on your roof, on their websites, I will put it on your roof. Right now none do, It's your property and your roofing warranty, I have no right to use you as a "test" project. Yet many of my competitors do just that. The only 100% Green method known to me, is power washing the roof with no chemicals, just water. A roof will sometimes come clean "looking" just by blasting the algae off. The algae was not chemically killed, so after pressure washing, the roof is still coated in living algae spores, which continue to grow strong and turn black again in a year or so.