Found a great cleaner to get rid of the mold/crud on top of the roof. Found at Lowes for about $25. 2.5 gallon jug makes 5 gallons of cleaner. <br/> Mix in spray jug, let sit 3 minutes and hose off. Claim can use just a garden hose but i opted for a quick hit with the pressure washer. Instructions state safe of fiberglass.<br/> The results are obvious in the picture.