Under construction here in North Texas. The leuders limestone wall has been up for about 15 days and some of the rock (about 6) has developed this dark ring around the edges. PB says this is natural for this type of rock, but I don't see it on peoples houses that have this stone, so why my pool wall?? It wasn't there when they built the wall, so this is something that has just developed over the last week. I don't want the rest of the wall to start looking like this either. The back side of the wall is exposed (unsealed) gunite at the moment, so I don't know if this has anything to do with it?? Any ideas??