Quote Originally Posted by Simmons99
stupid question - but have you tried pouring a 50/50 water bleach solution on it and letting it set? It could be like mildew - does it stay wet there all the time (like from a mister or water feature)? I get something like that on my concrete walk-ways where there is moisture and little direct sun.
I tried to power wash it no change, and I have poured bleach on it, but i did not really scrub it. There was no change. It does not stay wet.