errant pH readings ?

[Wheelman76]

I'm dealing with the same thing right now. My tank is four and a half months old and my ph has always hovered between 8.15 and 8.25 during lights on and it drops down to 8.05 to 8.10 at night and I run the light in my refugium 24/7. For the last three or four days the ph won't get above 8.12 during the day and drops to 7.97 at night. I know it's not a huge difference but it's bugging me. It must be the weather since we are both dealing with this problem at the same time. I have my balcony door open all day and night as I have for the last few months and have made no other changes, so I think it must be excess co2 causing the drop in ph. Btw my alkalinity sits between 8.4 and 9.0 and I have an apex controller that reads the ph , which I just calibrated three days ago when I noticed the drop. I plan on running a tube from the air intake on my skimmer out my window to see if it makes any difference.