Tropic marin bio calcium is a Calcium Carbonate supplement. So it not only adds Ca, but also slightly increases the Kh. The other noce thing about the product is that it contains all 70 trace elements (just like TM salt). A 13dKh is nothing to worry about, in fact you can safely run a tank at 14 if you want. As your Kh increases beyond 14-15 it tends to have such a stabilization effect that it inhibits your pH from increasing above 8.0-8.1, but it also inhibits it from dropping as well. This effect can be desireable to Fish Only tanks, or in aquariums with stressed or sick fish.

my advice is to roll with it for a few days, and discontinue superbuffer til needed.