Quote Originally Posted by SunnyOptimism View Post
I can see low pH as a definite problem especially if the carbonate packing fraction is high enough to allow the particles to form a connected matrix. Low pH would tend to convert the less soluble carbonate into more soluble calcium chloride and thus deplete any carbonate material in the near surface region of the PVC that is in contact with water. I bet if you looked at a sample of old PVC liner material that was exposed to low pH under an electron microscope in cross-section, you'd probably see a surface region of the PVC with depleted calcium and a bulk region with normal calcium levels.
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So, in summary, what does this mean for pool liners.......no idea! But this is The China Shop and I was told we are allowed to speculate here, so you all can draw your own conclusions.
Because we haven't had ANY reports of vinyl problems with little or no calcium in the water over more than a decade, the theoretical issue of calcium carbonate depletion from vinyl may be possible but in practice not an issue. Whether this is because the percentage of calcium carbonate filler content is below the 7% that the sources I had referenced indicated is the amount above which the characteristics of the vinyl become problematic, including susceptibility to acid, I don't know. This is consistent with what you are speculating, but again since we don't see problems in practice there is no need to worry people about it even by mentioning it as a theoretical problem outside The China Shop.