Odd jump in ph. What could have caused it?

[Keithcorals]

I did a water change today and before the water change my ph was 8.26 after it went to 8.5. I used Tropic Marin pro reef salt with an alk of 8. I did 20 gal in my 180gal system for a little over a 10% change. The alk in my tank was 7 before the change and tested 7 again an hour after the change. I took some of the water that came out of the tank for the water change and tested it with the ph probe and it still reads 8.26 so what could have driven my ph up?

 

[Randy Holmes-Farley]

Did the pH probe get exposed to air during the change?

Do you have auto top off that might have added limewater (kalkwasser) during the change?

Did the room somehow get a lot more than usual fresh air?

 

[Keithcorals]

I considered all of that but the prob was under water the entire time
I do have an ato but it holds only RO water and it was off during the water change
I have a pump that doses kalk but it was shut off before the water change and is still off
The room has not had any doors or windows open anymore than normal
Any other ideas?

 

[Randy Holmes-Farley]

Another possiblility is you moved something that impacted the electrical interference that the probe was (or is) experiencing.

I can't think of any other reason the pH would rise like that. In any case, a pH of 8.5 is not a problem.

 

[Keithcorals]

The ph slowly went back down over the rest of the day and is back where it normally is this time of day. I'll be doing another water change today and this time I'll pay closer attention to the pH to see if it happens again. I'll also test the pH of the new saltwater before adding it.

 

[Randy Holmes-Farley]

OK, sounds good. Let us know what happens.

 

[Keithcorals]

Well I found what did it but I still don't understand how. I started by testing the rodi water before mixing the salt in and got a ph of 7.9 not that that makes much difference in rodi with 0 Tds. I then mixed the salt in and let it mix for an hour before testing and got a ph of 9.65. That would explain the jump yesterday but I tested the alk in the newly mixed saltwater and it was 8.5 so I still don't know why the ph was so high. I did the water change and the ph in the tank went from 8.26 to 8.52 the alk in my system is still 7. The ph in my tank took almost 5 hrs to get back to what is normal for it.
What do you think?

 

[Randy Holmes-Farley]

Salt mixes can be designed to have a variety of different pH values before actual mixing and aeration. In the past, some have been above pH 9, although I've not seen any such measurements lately.

Next time aerate the salt mix longer and see if that helps. CO2 should be drawn in to lower the pH.

 

[captainsaquarium]

It might be best to mix your saltwater well in advance. I tend to keep some on hand and it's nice to have and alleviates this sort of problem as you can test it and perfect it before adding to the display. Happy reefing