Has anyone compared results from different test kits with those from a pool store? If so, which do you choose as your "ground truth"?
I have used several test kits at home (ColorQ, Pentair78DPD) and at a local pool store (BioGuard/Alex) with pool samples drawn at the same time and under the same conditions, and gotten different results from each test. The results were different enough that when I crunch the numbers to determine amounts of chemicals to add to the pool, one kit would suggest I add 1/2 bottle of acid, while the other suggested I needed 4# of baking soda.
With the ColorQ, I emailed tech-support at LaMotte, and received much of the same advice with respect to the wait times between adding the drops and taking the readings, and with the temp of the water. I adjusted my testing protocol (to the point that the coolness-factor of the ColorQ was greatly minimized), and still got different results.
SO - I'm still on the market for a test kit I can use at home that will produce results consistent with those I get from the pool store. Of course, the pool store could be out-of-calibration, so I plan to compare different pool stores in the next few weeks.
Has anyone compared the TF-100 with a professional system (like BioGuard/Alex?) What do you as your baseline?
Thanks in advance for your advice and suggestions!