Sam, feel free to delete this post and add/or change to top post to reflect these additions and changes.
Correction, Mg - Magnesium is a MACRO-nutrient
The Macronutrients are:
Ca - Calcium, C - Carbon, H - Hydrogen, Mg - Magnesium, N - Nitrogen, O - Oxygen, P - Phosphorus, K - Potassium, S - Sulfur
The Micronutrients are:
B - Boron, Cl - Chloride, Cu - Copper, Fe - Iron, Mn - Manganese, Mo - Molybdenum, Ni - Nickel, Zn - Zinc
Other commonly used abbreveations:
CO2, O2, H2O, NH4+ (ammonium) pH, (power of Hydrogen-the H is capital because it represents Hydrogen) KH, GH, TDS, DOC, DIC