MgO is poorly absorbed form of Mg. Best form is MgCl or Mg-Citrate
Take buffered Vitamin C. to make that add 1/2 tsp Baking Soda + 1/2 tsp Ascorbic Acid in a glass of water. Let the CO2 fizz out. The resulting mixture is Na-Ascorbate ( Sodium salt of ascorbic acid). U want to take that..
The reason why sea-salt is recommenede is because, it is high in Magnesium.