Sorry Jim....Ya got it backwards dude
You can use Epson salts (MgSo4) about once for Mg suppliment because the sulfate levels will be raised too much.
To keep your ionic balance, a mix of 1 in ten MgSO4 to MgCL2.6H2O is used.
........BTW dropping kalk is the typical way of this happening....Ca and alk but no Mg....which must be supplimented...a lot more than I ever thought too...PS Both Bev and I had similar events...culprit low Mg