This Wikipedia article explains that the black on roofs is a bacteria, similar to a plant.
So, when new "Gimmick Sales Products" come out, that say "Won't Harm Plants" you will know it won't kill that super strong plant on your roof!!
What plant do you know of strong enough to thrive under the conditions roofs offer? Shingles surpass 100 degrees in the summer and who knows how cold in the winter?
It lives through rainy weather and droughts.
That's why the roofing manufacturers never specify any of these "homeowner chemicals, sold online or in hardware stores to clean their roofing products-they know it won't work and may just cause damage to your roofing.
Read what the roofing manufacturers say to do to clean the black off. It's not Pressure Washing, Power Washing, Pressure Cleaning! In fact, they say specifically not to use such high pressure methods. Instead they say - Well, go ahead and read it on their websites yourself, right here on my website! = http://www.bergmanpressurewashing.com/Manufacturer_Specifics.html
Watch me clean with this gentle process here on Youtube-