No one at TFP was mixing anything up. It was a guy at a pool store who got it wrong and the poster at TFP knew that, tried to explain to the pool store person what a hydrocarbon was (i.e. CH is carbon with hydrogen attached) and started the thread as an example of the mis-information at some pool stores. The thread title was facetious.

Thanks Carl. That's really what I'm looking for -- real-world examples of older liners in pools with low CH with no problems and not seeing any examples of ones with problems, at least not in any higher proportion than in water with higher CH. Also, I wanted to let people know here that indeed there may be some calcium carbonate in vinyl liners so that no one says that there isn't. We can still give appropriate advice and say that lower CH isn't a problem, but we shouldn't say that vinyl liners don't have any calcium carbonate whatsoever. It would be nice to know chemically why it may not matter, but real-world positive results will do.