What are the black stains?
The black stains are caused by algae that grow on limestone, they are actually caused when the algae begins to decompose. Often, these black or dark brown stains are mistakenly thought to be dirt, tree droppings, mold, fungus or mildew. There are other types of fungi and algae that can also cause staining, like green stains sometimes seen on roofs. However 99% of roof stains are caused by Gloeocapsa Magma.
