CYA level-my test and pool store test

I took a sample of my pool water to get tested at the pool store and they told me my CYA was 100. This is a new pool this August and I bought the Taylor 2006K kit and measured the CYA with it when I got home from the pool store and the black dot does not disappear until I am overflowing the tester. This means that my CYA is less than 20. How could there be such a difference between what I measured and what the pool store measured. I just bought the kit in August from Leslie's. Could my reagents in the test kit be bad, or does the pool store have no idea what they are doing ? Which should I trust, the pool store or my test kit ?

Thanks

How much CYA have you put in the water? I suspect that it's nowhere near enough to get you to 100 ppm. If that's the case, trust your results.

If you go to 3 different pool stores you'll get 3 different results... It's a subjective test. I know it's hard to trust your own test ( it is for me for some reason) so maybe take a sample to a different store and see if you get a result that is more in line with a lower reading .


Have you added any CYA?

I remember reading posts on this forum where the pool store was computing 100 minus the actual CYA level due to misreading the test. And yes, if you are using a tester with marks to 20 and you overflow it and still see the black dot, then that means your CYA is less than 20. It's possible that your test chemicals are bad, but that's probably unlikely.

Richard

One thing you need to do with the black dot test is after you mix the reagent with the water sample you have to shake and wait before checking the dot. When I do the CYA test I mix, then do other tests and come back to the CYA test last. I have checked using the recommended method (I think) of observing the dot in sunlight while held at waist level, and also viewing down through the tube looking at fluorescent light reflected off a white paper....no overhead illumination. Results of both viewing methods are close enough for my purposes, better than +- 10 and that's at the 40-60 levels. I'm guessing at the +-10 but certainly no more.
Al