Hello, I just had my above ground pool installed last summer. When I opened it this summer it was clear as could be but within a week there was a large black stain across the bottom of the liner that would not scrub off not matter how hard I tried. I went to my pool store and was told it was a copper stain from using Kleen Pool algicide. They have had me dumping lo and slow into the pool to reduce the PH level and claim once it is under 6 that the stain will magically lift and go back into solution. I have now bought 4 8 lb canisters of lo and slow to lower my PH and the stain does not appear to be lifting (although it may be getting lighter I'm not sure). My PH is now at 6.3 and my alkalinity is extremely low because of all of the lo and slow I have used. Please help, how can I get rid of this stain without continuing to buy the lo and slow and how can I prevent it from coming back again? Thank you in advance.