I just dosed baking soda and it *lowered* my pH. Shouldn't it have raised it?

[sixline]

I have been trying to raise Alkalinity in my tank by dosing baking soda.

I added some this morning, then noticed on my Apex that my pH immediately fell. Shouldn't adding baking soda cause my pH to go up?
What does this mean? Was there a precipitation even of some sort?

 

[Albertan22]

The baking soda adds a bunch of co2 initially and drives the ph down. I think over the more medium term it will bring it up because of the alkalinity addition once the co2 clears the water column.

 

[T-J]

Just got this off the google:
You can use baking soda or soda ash to adjust the alkalinity and pH in your reef aquarium. Baking soda (sodium bicarbonate) will raise pH after an initial small drop. This temporary drop in pH goes away in a few hours. I believe this makes baking soda the best choice if your pH is 8.1 or higher.

 

[sixline]

The baking soda adds a bunch of co2 initially and drives the ph down. I think over the more medium term it will bring it up because of the alkalinity addition once the co2 clears the water column.

Interesting, thanks. I will keep an eye on it. I'm a new APEX owner and becoming a data nerd.

If you had to guess, when do you think the pH will rise?

ETA: Ninja'd by T-J. Thanks!

 

[Albertan22]

Interesting, thanks. I will keep an eye on it. I'm a new APEX owner and becoming a data nerd.

If you had to guess, when do you think the pH will rise?

I’d guess within a few hours. I’ve used baking soda to buffer ph in my qt when doing hyposalinity and it’s always achieved my ph change by the next day when I test again. I’m just using test kits for that. I haven’t attempted to use baking soda to alter ph on my DT with the Apex so never watched it that close.

 

[Randy Holmes-Farley]

Interesting, thanks. I will keep an eye on it. I'm a new APEX owner and becoming a data nerd.

If you had to guess, when do you think the pH will rise?

It comes back to where it was as the water is aerated. it doesn't really bring it much higher than that. . The raised alk brings it to a new equilibrium with the air, which may have a very small pH boost

Sodium carbonate (washing soda) is the thing to use if you want a pH boost as well as alk boost.


I show these results here:

Chemistry And The Aquarium: The Relationship Between Alkalinity And pH

Randy answers many questions in this complex relationship.

reefs.com

from it:

Supplement	Initial pH	24 hour pH	120 hour pH
none	8.10	8.11	8.21
0.5 meq/L HCO3-	8.06	8.15	8.33
0.5 meq/L CO3–	8.44	8.28	8.34
0.5 meq/L OH-	8.76	8.47	8.33
0.5 meq/L H+	6.91	7.91	8.15