My composite deck had little black spots and black streaks all over it. Cleaning it with the usual deck wash didn’t touch the mess. I searched online and found Corte Clean. Drove to Lowe’s and bought 1 bag of it. Followed directions given in the video and wasn’t sure there was much improvement. BUT, THEN IT DRIED!!! I cannot overstate how beautiful this deck is now. This product is worth every penny and I will make sure I always have some.