Calcium and Magnesium are both already in a every soil and almost every bottled/bagged nutrient line. I only add what's needed when it's needed. I let the plant tell me what it needs and when. Keep in mind that CalMag is a sales product/term. If you need calcium, I'd add calcium.. If you need magnesium, Id add magnesium. Adding both when only one is needed, or adding both when neither is needed, can lead to issues.