I do remember now Ben saying at one time that certain liners require a small bit of calcium in the water. I also did do a bit of playing around with the langelier saturation index, and if you subscribe that it's correct, it's impossible to stay out of the corrosive range without any Ca in the water. It seems that 100 - 150 is the range that keeps the index happy. I haven't researched it really all that hard, but I think i'm going to hit up some mechanical and chemical engineers at work tomorrow and see what they have to say.

Michael