need to test TA if PH/CH is ok?

I would. It's good to know because you can calculate your CSI and learn your scaling potential. It's less of an issue with vinyl lined pools (unless you have a heater) but it is still something that I would want to know.
 
It depends on where you live. In the arid portions of the country with which CH fill water and high evaporation rates you need to monitor CH levels very closely. If you live somewhere with high humidity and low CH fill water you can track CH twice a season along with CYA, Salt, and Borates.
 
JasonLion said:
If you live somewhere with high humidity and low CH fill water you can track CH twice a season along with CYA, Salt, and Borates.

that's exactly where i live - humid summers and extremely soft water.

as for TA, if PH is steady, is it possible for TA to go far out of range? I understand what can cause PH to go up and down and my understanding was the TA will change as a function of PH since they are closely associated. and if PH is good and steady, would that most likely mean that TA is also where it was before?

i'm not trying to be lazy and cut on testing - just want to understand the factors that affect TA.
 
TA should only change when PH changes or when you add fill water with a significantly different TA level. The main thing about TA is that it can sneak up on you, staying the same for a long time and then changing when you weren't really expecting it to. Technically there is no such behavior, but in practice if often surprises people.
 
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