I installed my Trex deck in 2011 here in Iowa. By 2012, it started getting black mold spots and other stains, especially under the maple tree over our deck. I searched around for the best composite deck cleaner and found Corte Clean. The black spots and other stains just disappear. Give it some time in the sun. Our deck looks brand new. I have been using Corte Clean spring and fall or when I notice new stains ever since. It is a good idea to not let stuff sit on the deck and leech into it and Corte Clean any stains when first noticed. Blow my deck off often, which only takes a minute or two. I just ordered my Corte Clean for my yearly spring cleaning and will again order this fall when I need it, to make sure it is fresh.