It seems some folks wanted an answer to why magnesium nitrate was suggested as a better choice than sodium nitrate for dosing a reef tank. In short, it would not be, IMO.
Good choices are sodium or calcium nitrate (calcium nitrate is actually a balanced alk and calcium addition system when the nitrate is consumed) as well as ammonium bicarbonate and chloride. Most of these are cheap and easy to get food grade.
Magnesium nitrate would boost magnesium each time it is added, in an unbalanced way to its consumption relative to alkalinity, and in many tanks it would rise steadily. That seems suboptimal.
Magnesium nitrate would add 12 ppm of magnesium for each 41 ppm of nitrate and 2.8 dKH of alk added. But consumption is not more than1-2 ppm of magnesium for each 2.8 dKH of alk consumed.
FOr further discussion, please start another thread. :)