There is this discussion over at Trouble Free Pool that has uncovered the apparent fact that granulated calcium carbonate is the common filler in vinyl pool liners. I thought I'd bring that discussion over here as well.

I think that in practice it's not an issue given no problems actually seen with many pool owners having low CH water and vinyl pools, but I had always assumed there was no calcium carbonate in such vinyl liners and that apparently is not the case. The questions are whether it actually dissolves in low CH water vs. being bound more tightly in the vinyl matrix and whether even having it dissolved matters.