Hanna checker ,digital
Calibrated before the test
Tested few times in row
7 is correct, I am testing readings with hanna checkerThis is a lit reef aquarium? It correctly reads pH 7 and 10 standards?
It just looks like noise to me. I think there may be a fundamental problem. pH in any reef tank cycles day to night, rather than skipping randomly up and down. Photosynthesis during the day raises pH, and it falls at night due to respiration but yours was at one point rising all night.