Hi Richard,
I don't track TFP's stuff at all so I wouldn't know. I think the other mods have a similar experience to mine, and I know Al and Lisa have vinyl liners. I'm 99% sure Jan does too, and we all never bother with calcium levels. Al's liner has got to be close to 15 years old, too.

You'll need about 15 data points before you can legitimately determine a statistical trend--too much noise below that.

Meanwhile, don't you have a scrap of liner around you can grind up and test for calcium carbonate? Give me a couple of more years and I may be able to give you mine!

Carl