I have always questioned my ability to measure CYA accurately, and have read the many posts here regarding test accuracy.
Especially useful was two-cya-kits-consistently-disagree-t37391.html?hilit=cya%20test%20error%20taylor%20cya
I have a Taylor 2005C kit and I have the CYA view tube that is supposed to make the test a bit easier.
I get quite repeatable results, but have I have never been convinced the results are accurate.
In trying to 'calibrate' my results I have used pool stores to compare my measurements.
Some pool stores match my measurements, but one pool store in particular always measures significantly lower CYA.
(All other tests are pretty close to my measurements)
In discussions with them they acknowledged they do not use Taylor test system (I'm pretty certain they use a Lamotte test system since my print out states 'WaterLink DataMate)
Unfortunately, this is the only store that I actually trust (Its a small independent Mom & Pop shop that have never tried to sell me anything that I didn't already know I needed)
Last year, as an experiment with the store, I purchased a small vial of Taylor R-0013 from them and asked them to test my water using both systems. They confirmed my result using Taylor, which if I recall was 30ppm higher than their test test results. They could not explain the difference except to say that they are not as experienced with the Taylor method to accurately determine when the dot becomes obscured, and that their experience in real life confirmed their results.
I have a SWG that requires CYA to be 60-80. This year, my Taylor kit consistently measures 40, while the store testing measured 80. It is not in the stores best interest to measure low as I think I need to by CYA from them and they are saying I don't need it. (they didn't try to sell me anything else)
Additionally, I have found that my best year for pool maintenance/algae was before I purchased my test kit, and relied solely on this stores CYA test results.
Is there a fundamental reason why Taylor and Lamotte tests results differ? or is there some other factor why the results would vary?