Calcium and magnesium deficiencies show up more often under LED than under old HPS, and autos in coco or light soil are the first to display the rusty spots and interveinal yellowing. The plants photosynthesize harder under the cooler light and use more of both, while filtered or RO water gives them none to begin with. Dosing guidelines for cal mag by medium and water source, and how to tell the two apart on autos, are set out on https://turboautoflowerseeds.com. Adding it from week two beats waiting for symptoms.