Suppress redox during with REACTION

[Flopi]

Hello,
I have a question on the REACTION block on redox.
I am doing the following: I have 2 solutions I am mixing, with certain quantities of ions, especially sulfate. After the mixing I need to add some sulfate. I used the REACTION keyword:

REACTION
SO4-2 0.00653
1
END

However, this causes the pH to drop significantly (from 7 to 2) and the reason seems to be the reduction of S. Is there a way to do this procedure without reducing my sulfate ? I tried to put both pe at 8 but nothing works. Is there a way to just add sulfate to the solution without the REACTION keyword ?

[dlparkhurst]

You should not add a charged species; in fact, REACTION ignores the charge that you put in.

Add a charge balanced reaction, like Na2SO4, and your redox reaction will go away. Essentially you added SO4, which reacted SO4 + H2O = SO4-2 + 2H+ + 0.5O2

REACTION
Na2SO4 0.00653
1
END

[Flopi]

Thanks a lot for the answer !

(I thought previously that it didn't solve the problem, but because I put NaSO4 instead of Na2SO4...) Now everything works perfectly