CMX is a calcium /magnesium additive used for preventing nutrient deficiencies.
As an added bonus CMX also contains the following trace elements;
Iron (Fe)
Copper (Cu)
Manganese (Mn)
Zinc (Zn)
Molybdenum (Mo)
Boron
CMX contains 6% calcium, 2% magnesium, 0.2% iron EDDHA (NPK 4-0-0) plus all of the other trace element (copper, zinc and manganese as EDTA, molybdenum and boron).