I get that but I also have corals that have struggled and are now responding since I've been focusing on rising my PH.it could be, but were also early in the day. my apex probe wont reach max pH until about 6pm. in fact, my pH right now is 7.97, so still, im not sure why youre chasing a number right now. on the further right two days, i had my windows open. this is to show the fact that the time in which you tested, is probably the reason for the lower number. if the probe matches the test, then i would suspect it has to do with the time of day. but, unless youre dosing something to keep it equal throughout the whole day, youre going to have high and lows. your highest wont be until at least the later part of the day. also to mention, the left two days i had a scrubber attached as well. the larger vertical lines is when i do my daily manual dose of alk. the furthest right day had a higher dose of alk than the day before. so thats why its kinda all over the place right now.
for example-
With that being said I believe PH is a huge issue for me. Prior to getting the Apex I never tested PH and when I did it was coming in really low even at its highest of highs. Even if the test kit says 8.0 that's still really low to be your highest level.
I'm basically choosing to believe the Apex. I'm investing a lot of money into this Neptune stuff. I've calibrated the probe and it's giving me exact numbers when dipped in calibration solution; that's good enough for me to feel confident in it.