There has been significant interest in roof washing lately, including a lot of questions about what to use to clean off those black streaks and stains (mold algae also known as 'gloeocapsa magma'). These stains will significantly affect the look of any home. In the past, the only way to get rid of them was to replace the roof. It has been estimated that as much as 50% of all roof replacements have been done because of the appearance of the roof and not actually because of its functionality.