Constant aeration makes it impossible to maintain BOTH a reasonable pH (< 7.8) AND a reasonable TA (> 80 ppm). Your pH of 8 is NOT 'normal'; rather it's driven by the aeration.
The sudden spike in CH could be a testing error . . . or it could mean your very low TA is resulting in dissolving plaster! NOT GOOD!
1. Turn off your fountain and water fall, unless you are actually using the pool. You'll need to maintain some circulation in the spa. If you'll post pump, filter and piping pictures we'll see how that can be done, without so much aeration.
2. Watch the Taylor videos to make sure you are doing the test correctly. http://pool9.net/tk-guide/ Then retest TA and CH.
3. Lower your pH to just below 8.0. At the end of the pH test range of phenol red, the values you get ~6.8 or ~8.2 do NOT mean your pH is 6.8 or 8.2. Instead they mean that your water's pH is 6.8 *or* below, or else that your pH is 8.2 *or* above. However, it's worse than that, since a lot of people can't see the difference between phenol red at 8.0 vs 8.2.
If it works out that you DO want to keep your pool at 8.0 . . . you'll need to get a pH meter, so you can be sure your pH is *really* 8.0 and not something higher.
Ok, this may get confusing.
. . . or not. I tried writing a more complete explanation, but it was turning into a China Shop type post -- too complex to be useful to 99% of folks.
Here's the bottom line: we need to help you work out a way to maintain your pool without damaging your plaster OR having to constantly add chemicals.
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