Please help! I have about 15 of these "stains" or "spots" in our white pool plaster. It was remodeled 2 years ago and had it re-plastered as well. The pool has a 5 yr warranty on the re-plaster. We've had many problems since the replaster (calcium nodules in spa and a 13 in crack in the plaster 11 days after the replaster, they fixed this by removing the panel and replastering that area). In the photo, the first spot to the left you can see a crack where the stain is. If you look closely, under all three stains or spots, you can see a fine line (rainbow shaped). This is a crack as well. I had a diver check the plaster and he said there are many "hollow" sounds in my pool, especially where these stains are. Can anyone tell me what they believe they are? Our pool is a chlorine pool. I'm happy to answer any questions in order to get some answers. Thank you!