Acceptable range of fluctuation of PH

[hampmp]

What is a acceptable range of fluctuation on PH? Mine usually travels between 8.09 - 7.90 over the course of a 24 hour period usually dipping after the lights go off as expected.

 

[kegogut]

In the past two weeks my PH has done about the same as yours. low end was 7.92,high end was 8.08