ph dropped from 8.4 to 7.8

[lionfish]

i changed my sump yesterday and now my ph has dropped .i was wondering what could it be . i put my two drain lines from the overflow going into a mesh bag with carbon and its inside of the water could that have anything to do with it ?

 

[ming]

What time did you test the PH? List first AND second time.

 

[lionfish]

i checked it today around 2pm and i did the change yesterday last night before i changed it i was steady at 8.4

 

[ming]

The PH is typically highest right before the lights go out, and lowest right before the lights go on. This is because at night, all the animals in your tank are releasing co2 which reduces the PH.
Does your lights go on around 2PM more or less a couple of hours?
Its a large swing, but its still within the safe range. If it goes below 7.8, I'd start getting more concerned. Make sure you have plenty of surface agitation at night and the skimmer is running at night to help oxygenate the water.
Test the PH again right before the lights go off to see if the PH is back up to prove the theory.

 

[Deep Dive Coral]

+1. My ph goes from 8.2 to 7.9 everyday

 

[OzoneParkGuy]

If you have changed to a bigger sump then that should mean you have added more RODI water to your system which is stripped of all componets causing a drop in ph. Which means you need to match what you already have in your tank to what your going to add to your tank.Usually done the night before. As suggested always check before and after. Do this aswell for every water changes so as to not stress your coral reef. The above mentioned is right on point.
Carbon will not cause this.