PH question

[seascape]

i was wondering i have a ph monitor the question is does your PH go up or down at night right now my PH is at 8.4 tank temp 78 degrees never raises above 79 degrees CA 420, Mg is about 1350 maybe a little lower, its 9:30 pm and my actinics are the only thing on,im old school and all this new monitoring equipment takes a little to get use to,whats funny im hooking up a new controller tommorow, oh what fun and you will see more questions after that.

 

[Semibfy]

Theoretically, Yes, During light hours CO2 (carbonic acid in water)) is consumed thus ph should go up as day progresses but when no light, no photosynthesis thus CO2 accumulates causing pH drop as night progresses. How much fluctuations, all depends on tank. Well equipped and maintained tank should not have major problems. That is IMHO and simply put.