I have a copper ionizer for a sanitation system versus salt or chlorine. I’ve checked all my levels and they’re always great. It has to be either some sort of metal deposit or I have read that there is a micro organism under the pool liner that is leaching through. I noticed this stain last year but it wasn’t nearly as bad and it is multiplying this year.  We installed a pool pump heater for the first time this year.  Which keeps the pool at 85.

The liner is 9 years old. I used to cover the pool with the solar blanket but now with the heater I’ve left it off for most of the summer especially when it’s hot.  I have tried an inhibitor but I think it’s too late for that.

I am attempting to shock the pool and see what happens.

Any ideas? I am going to replace the liner but I need to figure out what’s going on so that it doesn’t happen to the new liner. Any help would be great.