High TA but low PH?

[matasoj]

So in my testings of the water my TA has been consistently running 180-200. My PH has been running low for a while, usually in the 7.1-7.3 range. I turned the return jet up so it sprays up to the surfance and aerates it. Most of the comments I have read seem to be implying that PH and TA track together, e.g. if one is high the other is too. That's not the case with me. PH is low, but TA is high. I added Soda Ash this morning to bring the PH up, but now that the PH is up to 7.4, the TA is way up to 240.

This leads to my questions:
1) I have a vinyl above ground pool. Does TA matter? How much does it matter?
2) The instructions in the app say to lower TA and PH with acid. I bought a jug of liquid acid, but it looks like nasty stuff, so I'm wondering how much I need to use?
3) Is it normal for the PH to be low while the TA is high like it is?
4) Does aerating the water with the return jet really raise the pH on it's own? or does it do that ONLY in response to lowering the TA/PH with acid (e.g. some chemical reason)?

The water is clear, it is enjoyable to swim in. I have been running the pool vacuum robot daily so the pool is nice and clean.

Current pool stats, according to the Taylor K-2006:
FC: 2.4 (I added 75oz of 7.5% bleach after that measurement was taken)
PH: 7.4
TA: 240
CH: 130
CYA: 40
WATER TEMP: 81º
CSI: -0.09
Air temp: 86º
Pool size: approx 16000-18000 gal (different calculators give me different sizes for some reason - but it's round, 27' across and 48" water depth)

 

[PoolGate]

Here is a good article. Lower Total Alkalinity - Trouble Free Pool

 

[mknauss]

I have a vinyl above ground pool. Does TA matter? How much does it matter?

The primary issue with high TA in your pool type is a rapidly rising pH. If you do not have that, do not stress.

The instructions in the app say to lower TA and PH with acid. I bought a jug of liquid acid, but it looks like nasty stuff, so I'm wondering how much I need to use?

PoolMath Enter your test results. When the pH rises to 7.8, lower it to 7.2.

Is it normal for the PH to be low while the TA is high like it is?

Only if acid or acidic products are being added. Otherwise the pH will rise pretty quickly, if any aeration whatsoever is occurring. Swimming in the pool creates great aeration.

Does aerating the water with the return jet really raise the pH on it's own? or does it do that ONLY in response to lowering the TA/PH with acid (e.g. some chemical reason)?

It does. The pH will not go much higher than 8.4 or so without chemical addition. And you do not want a pH that high.