Do I have an Iron Deficiency, if so How do I increase Iron levels (Already using Calmag)

rain water is a bad idea. especially if downwind from any city or industrial area. usually quite acidic and god knows what is in it. your tap water will likely provide the iron you seek. may even reduce need for cal-mag too. it will reduce need for cal mag in most contexts, i should say. you may need to dose and acid/base needed to correct pH... or not.. you'll want to re-measure if it is impossible to avoid, i'd check pH more often. may need more reservoir changs etc etc.