Hi everyone! I had a gentleman from All Brite Softwash call and inquired about cleaning a slate roof with greenwash. He has removed a black mold looking material but underneath is a orange non organic stain. We recommended F-9 BARC but he said it looks more like algae. We mentioned using agitation, he responded that it is chipping away. The roof is gray-blueish and he tried Terra wash but he didn't continue because he didn't see a change on the surface after using it. He is using Greenwash at a 4% and Bleach 3%. He has a cradle skid. We responded that tile roofs are the hardest surfaces to clean because you have to clean a specific way. It has to be cleaned on all four sides. Lastly we mentioned that he should let the homeowner know about the area that has that stain because it may be an old surface. Any additional suggestions???