Do you have metals in your fill water? If so, which ones? If you're not sure, take a sample to your pool store and see if they will test for them. Is the inside of your toilet tank stained brown, if you filled the pool from your tap water?

Try putting a vitamin C tablet on the spot and see if it changes in appearance. Also, please post a set of test results on your water, taken with a drop-based kit (no strips!!) for us to look at, and that might help us advise you better.


Welcome to the forum!