We installed our supposed no maintenance expensive Trex deck 5 or 6 years ago. Within a year, it started getting black spots all over it. I had no idea what it was. I tried several deck cleaners from the local stores. Nothing worked. I then went on the internet and searched. I found Corte Clean, called the company and they explained what was going on, with the black mold and how to clean it and keep it clean. I purchased the Corte Clean and cleaned my deck. It took a more time and Corte Clean, the first time to get clean. I could see all the dirt and mold coming out of the deck. The black spots disappeared. I now proactively apply Corte Clean in the spring, middle of summer and in the fall or when my deck starts to look dirty. This requires one bag of Corte Clean per year to keep my deck clean. Here in Minnesota, we just received two feet of snow two weeks ago, which has since melted, after a long winter. My deck doesn’t really look that bad, but I just re-ordered Corte Clean for the spring cleaning, which I generally do at in April or May when the weather permits. Corte Clean is a great product for keeping Trex decking clean.