Whoa, Guys, you've misread his posts (not that I've ever done that in my life )

The "pool" side of his exchanger is stainless steel...not copper. the "boiler" side is copper and it never touches pool water.

Secondly, I'm a little mixed up. Using muriatic to clean up an acid caused stain doesn't make sense to me. I'm missing something but I don't know what.

Off the subject, but muriatic is quite good at removing green masonry.....it's effectiveness diminishes as the masonry cures.

Dave S.