look up the improved diy two part system by dr randy holmes Farley.
it uses calcium chloride for calcium, baking soda for alk and magnesium chloride +magnesium sulfate (Epsom salts) for magnesium. calcium chloride and magnesium chloride is sold as an ice melter for sidewalks in winter. calcium chloride further speeds hardening of concrete so check redi mix concrete places.
that said also check you test kit, and also test for alk and magnesium as well.
the two part system does a one time correction to get things in line. then you dose equal amounts of calcium and alk mixtures when alk drops. After using up a gallon of the calcium/alk mixtures you dose the magnesium mixture.
my .02