Attached are the images of the problem areas of my 16 yrs old Pepple Tech Pool. One shows the problem area and one shows the adjacent normal area and one shows both area at normal view (just to see bad it looks). I called the original contractor and after looking at it he said nothing is wrong with the plaster, just black algae (which I do have in other areas). What I see is the plaster in the problem area came off causing gaps between the stones. They said they can not repair (replaster) and recommend acid wash. Can you please look at the images and tell me what you think so I can take proper step to have it repaired.
Thx
Thx