DID I FIND THE SOLUTION??? My 10 month old TREX deck is loaded with black dots of (mold??). After reading the years of accumulated forum comments,I decided to try something off the wall. I cut the top of a lemon and squeezed the juice over a 6x6 inch area. I spread it around with my fingers. It sat for ten minutes and then I scrubbed the area with a stiff hand brush. After 10 minutes more, I scrubbed the area with a few drops of kitchen detergent/soap. I rinsed with water from a bottle and PRESTO!!! The entire area is spot free, exactly like new. I intend to buy some citric acid in crystal or powder form to attempt to duplicate my experience. I will post the results ASAP