Under construction and noticing rust-like discoloration on my waterline tiles. It's primarily on the house side of the pool and the deep end whereas the other side/end of the pool looks alright. Spraying it with a hose didn't do much.
Could this be rust? If so, what would cause surface rust on tiles? Just sent my builder an email for his thoughts. Are there any means, tests, methods I can use to confirm what this is?


Other end of the pool not exhibiting the same discoloration.

Could this be rust? If so, what would cause surface rust on tiles? Just sent my builder an email for his thoughts. Are there any means, tests, methods I can use to confirm what this is?


Other end of the pool not exhibiting the same discoloration.
