Salt Change = PH Drop

[Z06-Hec]

So I have always used Reef Crystals by instant ocean and my PH has always remained consistent at 8.08-8.22. Recently someone sold me on changing to Crystal Sea Marine Mix, how this is what aquariums use etc its one of the best salts out there…. etc….
So i used it for the first time this Wednesday and did my normal 35 gal water change. Today Friday my PH has dropped to 7.85.
Nothing looks affected in the tank but that is a pretty significant drop no ?

 

[maroun.c]

How did the new saltwater test for Alk?
I make sure to test a new batch of salt or a new salt before use.
Normally if the new salt PH was low it could cause a small drop which would normalize after few hours. It could be that the new salt ALk was low which dropped the alk of the tank which caused PH to drop significantly due to surrounding CO2, assuming that you didnt make any changes (closed windows, heaters...) since then.

 

[Randy Holmes-Farley Verified Community Expert]

I agree that the only way a salt mix will impact pH in the aquarium after aeration has stabilized (and it may not be yet) is via alkalinity.

 

[Z06-Hec]

i didn't even think to check it before doing the water change….
I just checked and it did go down about a point from 9.3 to 8.4.

 

[Randy Holmes-Farley Verified Community Expert]

Alkalinity declined? That would result in a small pH drop if fully equilibrated with the same air.

 

[Z06-Hec]

yes Alk went down with new salt… it was around 9.4 with reef crystals and went down to about 8.3 with the new salt...

 

[Randy Holmes-Farley Verified Community Expert]

Then that might explain a small pH drop.

 

[maroun.c]

Can you check the alk of a fresh mix of the new salt? Presume it'll be even lower to cause your tank alk to drop one point.

 

[Randy Holmes-Farley Verified Community Expert]

I agree, the new salt water alk would have to be a lot lower to get a 1 dKH drop from it, and the alk drop doesn't explain the whole pH drop either. Testing error or other changes like the room air may be more important.

But there's nothing else that goes into the pH: CO2 and alkalinity.