Nope, that's the gist of it - 3:1.
My target parameters for this tank is Alk 7.5-8, Ca 400-420, and Mg at 1350-1400. The Mg is higher than the 3x, but I've always ran and prefer to run it higher than 3:1. The alk is higher than I prefer, but the tank has been settling in at around those values...