Is it also possible that the interaction with the CO2 in the air is causing the water to seek a 'natural' pH based on the alkalinity? If so, it may be advantagous to lower the alkalinity even more if I can get the pH to stabilize at a lower level than 7.6.

In an aquarium, the lowest alkalinity recommended is about 60ppm in order to prevent a pH 'crash' - a sudden drop into acidity. Is there a downside to run it that low in a pool?