pH up: when to add

[The Mermaid]

My pH is a little on the high side. It normally stays around 7.5, but sometimes it starts creeping up close to 7.8. I have some pH down to fix it, but wanted to know if it was OK to put it in at night when I add my chlorine. Or is it best to space things out. I wanted to put it in now, but I want to swim in a couple of hours. I'm thinking that might be dangerous though b/c I don't know how long it will take to become completely diluted in the water. Any advise? When do you normally add this stuff?

Oops, edited to add my other info, not sure if it is all relevant to the question though:

pool is AG 28ft w/dished out deep center, approx 22,000 ga.

Using BBB methods

FC 6
CC 0
TC 6
pH in between 7.5 and 7.8
TA 100
CAL 190 (vinyl liner though, so irrelevant)
CYA 35 - 40
temp 81