I am REALLY struggling keeping my pH in line and pretty much adding bleach each day (not sure if that's expected/normal?). With your current TA levels, your pH swing is expected. As your TA comes down, your pH swing will reduce. Additionally, your pool is realtively new and your plaster is still curing, so that also contributes to your pH swing slightly. Maybe I need additions twice a day? What is your daily FC consumption? Latest updates below.
I had pH at 7.8 on Aug 3 evening, added some acid to get down to 7.4 target, and when I checked Aug 4 evening it was really hard to read (didn't really look like any of the comparisons - but both wife and I agreed it looked closest to 7.5, so I logged that and didn't add any acid.) I checked on Aug 5 evening though, and it's already at 8.2.
Also like to add that we noticed on Sunday a white calcification (I guess) on the waterline tile where the spa spillway goes into pool. The spa spillway will also contribute to pH swing. Again, pH swing will reduce as TA reduces. Wife scrubbed it pretty hard and it came clean, but just noting that in relation to all my readings (hadn't noticed it before then). Sounds like I need to address CH but don't want to lower TA too rapidly, but I'm having a hard time lower TA at all, if my fill water is high in TA. Your current TA is contributing to high CSI, increasing your scaling potential. However, with a plaster pool, you will need to increase CH slightly as your TA comes down.
Reading #7 (Aug 3 - morning)
ph=7.5
FC=5.5
CC=0
TA=220
Fill water TA = 280
refilled water
added 12 oz 10% bleach
Reading #8 (Aug 3 - evening)
ph=7.8
FC=4.5
CC=0
37 oz 10% bleach (target 6)
57oz 31.45% muriatic acid (target 7.4)
Reading #9 (Aug 4 - evening)
ph=7.5
FC=4.0
CC=.5 (1 drop clears it)
TA=170
75oz 10% bleach (target 7)
Reading #10 (Aug 5 - evening)
ph=8.2
FC=5
CC=.5 (1 drop clears it)
50 oz 31.45% muriatic acid (all I had, shooting for 7.5)
55oz 10% bleach (emptied bottle, shooting for 7)