Magnesium isn't so easily absorbed-
http://www.magnesium.ca/magnesium-ab...bsorbing-salts
"The chelated magnesium bis-glycinate and buffered magnesium bis-glycinate (the same materials we use) were much better absorbed than other forms like magnesium citrate and magnesium oxide on its own."
Best way to absorb magnesium is to soak in a bath with magnesium flakes.