Just out of curiosity, what is your magnesium level reading? Whenever I run into this when starting a new tank, I raise the magnesium between 1500 to 1600, and it dies off on its own. I used to believe the Kent Magnesium was the best to use for use, but I've been using Continuum or Brightwell with the same success.
Me? My mag has been 1350-1410 since September, last one being only 1260 on 11/7 after I switched to mixing salt at home. I was supposed to test again today but I’m going to do it tomorrow before the water change.