Kalk Q?

[Aquattro]

The high pH is a result of the OH ions, which are not part of a typical Ca additive. Now you could add a very small amount without affecting pH (dependant on alk levels), but I'm not sure you could add enough to significantly affect Ca levels. I've never used CaOH to raise levels, only maintain them on a drip top off system. I'd probably not try it without doing a whole bunch of math first.
I did the math once before to figure out how much muriatic acid I could add to the tank without affecting pH (aptaisia control) and it was a very small amount in a 90g system.