On my old tank it’s always high the day highs and night lows and the trend in the up down. So this is very odd. I rain a co2 scrubber on old tank too. If it’s accurate then I’m fine with that number I’m not complaining about 8.3 it’s just idk if it’s accurate or not. I’ll see if the trend goes towards a night time low or notYou seemed concerned about a .01 dip with the lights on. I wouldn't doubt that you breating on the tank( for hours?)can give a .01 difference in ph. But really, I was just poking fun at you
So perhaps your ph really is high and steady with the co2 scrubber on skimmer intake. and cleaning the probe and recalibrating brought the reading to 8.3. Then you kept blowing your hot breath in the water and now its 8.29.as good of an explanation as any. Not that I would be concerned...

as good of an explanation as any. Not that I would be concerned...