Black algae?

[kpinpoway]

Black algae or stained plaster? What should I do?

 

[AftonJeeper]

First thing you need to do is find out what kind of stain it is. Place a trichlor puck on it to check if it is organic, if that doesn't work crush up some vitamin C tablets and place them in a sock on top of one of the stains. If that lifts the stain then you have an iron stain.

 

[kpinpoway]

Ok so after talking to a local pool veteran (45 years in biz). He said there is a water table under the area that can seep through and cause discoloration. He replastered it 12 years ago. He is going to take a look for me. I will post the results...