kalkwasser and vinegar?

[Aquattro]

George is correct. Acetic acid (in the amounts used) does not affect the pH of the CaOH2 solution. It merely increases the solubility of the calcium hydroxide. It also allows for a more complete reaction, making the solution less likely to precipitate. This, I believe, is due to the available carbon in the acetic acid molecule.
When I dosed kalk, it was in my make-up water, which ran all day. No adverse pH swings were observed.
Craig has all the info you'll need for a better explanation of this.