A change in pH from 7.5 to 7.7 might cut down your rate of CO2 outgassing by almost half and cut the acid demand in half, but a change from 7.5 to 7.6 shouldn't be so dramatic as having virtually no pH rise in a week. I'm sure something else has happened coincidentally (maybe something simple like there is less wind). At any rate, the point is that you can live with a higher pH and this will have you add less acid and that is what you are seeing (albeit more extreme than expected).

Richard