Why not feed acid directly to Ca reactor?

[H20ENG]

Hi Randy,
I tried a search, but could not find an answer....
I was wondering why straight acid could not be used to lower the pH in a reactor, rather than CO2? With the right doser and pH controller, could it not be done safely? If so, Which type of acid would be the best.
Thanks!
Chris

[boxfishpooalot]

The acid will reduce the alkalinity while Co2 does not :)

[H20ENG]

Carbonic acid in the reactor works different than sulfuric or muriatic? Why would the carbonic acid not reduce the alk as well.

Not doubting, just trying to understand:)
Thanks,
Chris

[Randy Holmes-Farley]

Yes, carbonic acid is different.

Adding CO2 cannot ever reduce alkalinity, because bicarbonate is produced when it looses a proton:

H2CO3 (carbonic acid) ---> H+ + HCO3-


So the net reaction is:


H2CO3 + CaCO3 ---> Ca++ + 2HCO3-

If you used HCl, the net reaction is:

2HCl + CaCO3 ---> Ca++ + 2Cl- + H2O

The last reaction is the same as adding calcium chloride. If you used sulfuric acid, you net calcium sulfate, etc.

So for a reactor, CO2 is by far the best.

one may be able to use certain organic acids (like acetic acid/vinegar), with the net being like the addition of calcium acetate. Bacteria break down the acetate into H2O, CO2, and HCO3-. That might work, but the engineering is complicated and O2 consumption is a concern. Salifert sells a product that is mostly calcium acetate (Salifert All In One).

[H20ENG]

Well there you go! Thank you for the perfect explination:)
Chris

[Randy Holmes-Farley]

You're welcome.

Happy Reefing. :)