Best Guess Table

[aquarium]

No, I aerated the water and simultaneously added acid to intentionally push down the alkalinity, which has resulted in the water stabilizing at the lower pH as well.

I'm not sure about the chemistry at the water surface, but all other things being equal, it appears that the recommended alkalinity range of 80-120ppm will yield the recommended pH range of 7.2-7.8 in a fixed relationship. 80ppm yields 7.2 pH, 120ppm yields 7.8 pH, etc. (at least in my pool )

EDIT:

Though an alkalinity of 100 and pH of 7.4-7.5 works fine for my pool, your pool may be very different and need different parameters.

Which is consistent with my experience of the relationship between pH and alkalinity through that range. END EDIT

BTW, I want to run the pool close to 7.2 pH in order to get the most benefit from the bleach. You said:

At a pH of 7.5, FC of 3.0 and CYA of 30.0 (and TDS of 550, Temp of 80ºF), the HOCl is 0.045. At a pH of 7.2, with everything else the same, the HOCl is 0.052 which is not a huge change, but is still about a 15% change.

Is there a reason NOT to run the pool at 7.2 pH?