It is not unusual to find my pH low in the A.M.. 7.8 I don't really get too concerned about!
pH will climb as the lights come on, and drop after the lights go out.
A properly calibrated pH meter will get my vote over any strip or color test at any time. i.e. two people can look at the results of the same test and come up with slightly different answers.
The main problem with using pH meters is the calibration of them. First, it takes a bit of perseverence to keep going back and forth between the 7 and 10 until it is stable, and, even when checking the sample you have to wait for a while until it is stable.
Many standards used for calibration are not worth using. This is based on a report by Randy Holmes-Farley, resident chemical forum person on Reef Central, who tested a large number of standards and found most to be wanting, as far as accuracy goes.
I forget which ones in particular were best, but I know, since that time, I have only purchase standards from a scientific supply company.
A search on Randy's site would probably reveal a thread about it.
OK, I found a link in my files to his article.
ON pH TESTING by RANDY HOMES-FARLEY
Another thing I discovered in my own case on low pH was in winter with the house shut up, the tanks weren't getting a proper air water exchange.
To see if this is the problem, take a sample of water after testing, and put it outside with aeration for an hour or two, and, if after that, the pH has risen, you know you need to get more fresh air supply to the top of the tank.
i.e. open windows, install fresh air vent, install HRV...........
