Pool store test results are mostly untrustworthy.

What you have to understand is that it HURTS their business if they provide accurate results. So mostly they provide INACCURATE results (incorrect measurements) that are very PRECISE (lots of decimals -- 2.03 ppm instead of 2 ppm) that SEEM really accurate, but aren't! To be fair, there are some store that do test accurately. But, the only way you can tell is to test accurately yourself (K2006) and compare. But, once you can do that, it's easier and cheaper to test it yourself, than to drive to the store!

Bottom line: if you let them do the testing, you'll almost certainly remain a 'victim' of pool industry marketing.