In waiting for Ben to reply, I have taken a photo of the stain that is developing in my pool. I think it is probably iron, but I guess it could also be copper. I did the ascorbic acid test today. Here is my photo:



Will the HEDP lift this stain, or does that just take metals already in the water OUT of the water? I am thinking that I will need to treat the stain. Stain treating products have specific recommendations for pool chemistry, and unless there is some miracle product out there, I won't be reducing the CYA by the amount needed. Any advice would be great - thank you!!