Uhm...dangit you chemists talking over my head.
I'm kidding.
To clarify, I ran out of plain calcium and only have calcium with magnesium in it. My magnesium is at 1475 ppm, so obviously I don't need to add any more magnesium.
So I was hoping I could just add a Kalk slurry, but from these posts it looks like I would cause too great a pH spike as I need to provide about 20 ppm calcium and 1 dKH per day.