I mean it’s very likely the stores will each have a different result. Check some of the threads here where people do that. One person was told the CYA was so high at 100ppm they’d need to drain the pool, but the testing with their own kit it was something like 50ppm. That’s a huge difference.
if the dot never disappears, then the CYA is lower than 30ppm.
I must not be communicating clearly, my apologies, here's what I'm saying: My pool builder added enough CYA to get to 50ppm, tested, and told me that was the result. Then I take it to Pinch A Penny and they use a similar CYA test as me (subjective eyeball), and they get 50. Then I take it to Leslie's and they use their automated one and get like 52.1 or something nonsensically precise. Then I take it to a different Pinch A Penny and a different guy does an eyeball test and also gets 50.
Then I add a certain amount of CYA to bring it to 60 and take it in and everyone measures 60.
This continues to happen weekly for 3 months meaning different eyeballs, different tubes of chemicals, same result. Everyone is ending up with the same thing a solid dozen times.
So I'm not saying different pool stores are getting different results and I'm not sure who to trust. I'm saying they're getting roughly the same results as my Taylor kit for all values, and with CYA being the subjective test - they're still remarkably consistent across people, chemical batches, and machines.
So I have learned roughly what it's supposed to look like when I'm supposed to mark it, even though I can still see the dot well past it. Admittedly I definitely exaggerated about it NEVER disappearing all the way to 0 lol. I'm just saying I intentially go well past what I KNOW it is and still don't have a hard time making out the black dot when under direct sunlight.
I've definitely seen those nightmare threads you mention about pool stores being horribly wrong about CYA (and other measurements). I've done my best to read up on proper methodology checking CYA and people talking about what works for them. I get the "glance" thing, I've seen the discussions. I still don't feel CONFIDENT about this test simply because I can still see the dot past the result that is even possible for it to be.
Just messes with me a bit.