So, got bored and was doing some math earlier and I came to realize something. GH's CaliMagic supplement is by volume, 5% calcium, 1.5% magnesium, and at their recommended dosage of 1mL per liter, you end up with a solution of 50ppm-Ca and 15ppm-Mg.
My tap water is ludicrously hard, over 600ppm...