How to control PH at night ?

[Lampshade]

I run a reactor and don't worry about it. I started to worry a little more recently since i my PH was going down to 7.5, which was a bit too low. So i started adding kalk into my top off water, now i sit at 7.8ish. The kalk made swings worse since it boosted my PH when water was evaporating during the day. I'd stay away from it unless you have to. I highly recommend a refugium, it's helped my swings a lot. here's the past week(the spike was me messing with the program). my high is about 0.2 more than the night, so not a huge swing at all.