I just set up my DIY co2 reactor for my 29g tank.
Prior to addition of co2 the pH was ~7.6 and KH about 3 to 4
After half day of CO2 I tested pH at night B4 turning off the lights. pH 7.4

In the morning, just after turning on the light pH was 8.6!

Testing an hour later yielded a pH of 7.6
and KH still about 3
Should i be concerned or surprised by these swings in pH. I would like to
think that the high ph test was not due human error, (i am a chemist), but
it is possible.
your thoughts?