nightly ph drop

[rickwaines]

So

I am used to a drop ph pH at night. My sump has no lit refugium which can mitigate this.
But in the last few days the nighttime pH as told by my probe has been dropping from 8.2 to 7.8 7.9. In the past few months it has been fluctuating from 8.4 at end of photo period to 8.1 before photo period. I have checked it with test kit but it usually is accurate.
My tank is about 8 months old and I have recently gotten my phosban reactor on line properly. Previously I was running it in a reactor that I that I am pretty sure wasn't working properly. So, I have been battling phosphate a bit but it is now dropping. The rowa phos says that I can expect a lowering of the pH initially and so perhaps this is simply what I am experiencing.
I have also begun vodka dosing as well
But I thought it would be good to check in with the hive mind.

So the two things that have changed is a proper phosphate removal system and vodka dosing.
I dose two little fishies two part c balance.
tank is a 40 g cube with skimmer.

params
kH 11 and stable
calc 450-470
mag. 1380
phosphate .015 ish
spec grav 1.026

Thank you in advance, Rick