I sure this has been asked before, but I'm curious, and pose the following hypothetical situation. All of your test numbers are out of whack. What do you handle first?
I ask this question partly because I fully expect my numbers to be very wrong (given I was using the pool store as my tester, and I was taking water from the very top of the pool), but mostly because I know adding some chemicals to address one issue often after another (such as adding CYA affecting TA).
(Some hypothetical numbers)
10,000 gallons, vinyl, SWG
Temp: 62 degrees F
Given my limited knowledge but extensive reading here over the past few weeks, I'd do things in the following order:
Lower pH (which will also lower TA)
Add Chlorine (using Cal-Hypo)
Lower TA (if necessary)
Testing in between steps, of course. How does that sit?