Since coming to this forum, I only go to the pool stores to buy salt or muriatic acid. For kicks, though, last week I took water samples to the two pool stores nearest my home. Earlier this summer, I learned that their methods and tools weren't better than my Taylor K-2006, and their advice wasn't better than what I found in this forum.

So Pool Store #1 gave out readings which, surprisingly, matched pretty closely to my own readings except calcium hardness -- they read my water at 375 (my weekly tests show CH is 260). Then, next day, Pool Store #2 gave me their readings which, surprisingly, matched pretty closely to my own except calcium hardness -- they read my water at 175, telling me I need to buy stuff to increase the CH.

So, my CH = 375, 175, or 260.

Wanna guess which number I trusted to be the correct reading? ;-)