I see so many times folks see "Cal-Mag" Deficiency and add more Cal-mag and get no result. The plant not taking up Calcium and or Magnesium is a symptom of an underlying problem. Too much Potassium will lock out Cal-Mag and a few other micronutrients. This is common with many growers. They switch to flower and poor on the potassium. Of course other things can lock it out - too frequent water, PH etc.
If you add Dolomite Lime to your soil to start - you should never have to worry about adding CalMag - if the plant starts showing signs of deficiency - look for the underlying problem as you know they have enough CalMag