I had read positive reviews of this product, but it exceeded my expectations. It cleaned up algae, mildew, and moss from numerous surfaces around my property - natural stone, wood decking, real stucco walls, etc., etc. It worked equally fantastically on all materials and in days (rather than the weeks that the label promised). I am now optimistic that it will do as promised, and completely retard the re-appearance of the algae, moss, and mildew. This is one of the best products I have ever used. No scrubbing - just spray on with a garden sprayer and leave to dry. Terrific!!