What I've seen is generaly people mix them to create a magnesium solution to dose and not dose one or the other.
I don't have a bottle of it handy, but the instructions are on the back of a BRS container. If you dose with kalk or a calcium reaector its one ratio, but if you dose with 2 part its another raito for Mag. I tried to look on their site but didn't see it quickly.