I had a marcite job about 4 years ago and almost immediately I noticed gray discoloration.  It has gotten larger over the years and is now a eyesore.  I was told by the pool guy that it's either black algae or bad chemistry and he won't do anything.  FYI, it is neither of the problems stated as I have always maintained the pool religiously.  I know he was adding a lot of calcium carbinate to the plaster and have seen that too much CC will cause this gray moddling to happen.  Has anyone been through this and is there an easier solution than an acid wash (will degrade the life of the plaster) or a re-marcite job?

Thanks in advance for any input.