I get the same results when just adjusting my feed. Epson salts are really really cheep. But used as a drench. You see results in less than 24 hours. The uptake happens in the dark.
Calcium is a different problem, because how plants transport calcium. Tomato growers with blossoms end rot know calcium management a pure nutritional issue. Adjustments to the base CLF schedule solves the problem.
The issue is are you see a calcium issue or a magnesium issue or a pH issue in your growth medium.
Calcium is a know limitation in hemp. Lots of work in calcium in hemp. Calcium is need for good dry weight. So I change my fertilizer to be a N-K-P-Ca. I need to pay as close attention to all 4. Not just Nitrogen.
Magnesium is used in other organic metabolism paths. I generally see chlorophyll reabsorption from older leaves long before I see magnesium deficiency in the new leaves. It is an easy correction. If you see it in one plant of a species, the rest of the plants have the same problem but just not showing it yet. Some plants are great indicators for magnesium availability. We used petunia as an indicator plant. It shows magnesium problems before everything.
For me and experience, if magnesium is a limitation we have a pH problem and not a magnesium problem.