We installed our TimberTech deck in 2008. It started getting leopard spots this past year, as we had an unusual amount of rain this past spring. Some areas were turning solid black with mold! We tried ammonia and hot water, Tide and Windex glass and patio with no success. We then tried Corte Clean. It was turning green when we applied it and the leopard spots just disappeared. I even recommended it to our friends that have the same decking, installed the same time, with the same problem. This product works really well here in Minnesota! I will be using it later this fall and again to keep my deck clean.