I didn't notice them until this week... But my deep end has a bunch of small leaf size dark brown rust colored marks... I thought they were piles of dirt or leaves at first... But scrubbing them with my brush did nothing to the marks. I am gonna run a full test of my water tomorrow in the AM.
I was curious why they only showed up at the main drains... I do have copper plumbing only return lines only on the far side of the pool. The main drains back to the skimmer and pump are all newly installed PVC. My white plaster is less than a year old and this is the first I am seeing these stains.
Sorry for the bad picture but they are in the deep end and pretty small. I figured that if my copper pipes were corroding the stains would most likely show up near the copper return lines on the side wall. But no staining to be found there. Only near the main drains.