Strange PH pattern
I recently purchased and setup in my planted tank a Seneye device. Prior to this I monitored my water with regular water testers and my PH in my tank has been 6.40 PH since I setup the tank. I know that that PH is acidic but my tap water is PH 7.2 and I have in the past checked my PH after water changes but it always maintains a steady 6.41 PH.
Now for the weird part, my Seneye device gives me reading on PH every hour on the PH of my tank and I have started to notice a trend. At 9 a.m. when I would check the tank normally with my liquid solutions my PH is 6.41 but slowly during the day about by .01 my PH every hour climbs to about 6.61 until midnight then slowly goes down to 6.41 at 9 a.m. the next day. Is this normal ? What could be causing this if it isn't ? I do have a CO2 unit that I run during the day but I shut it off after my lights go off at night could this be causing this ? My fish don't seem to be effected by it should I be concerned ?
Thanks for all the responses in advance.