Epsom salt contains a lot of magnesium and some use it as a part of their nute regiment. Do you know why you are mag deficient? I ask because I am curently mag deficient as well but mine is caused by ongoing pH issues... In my case adding mag won't help until I get the pH under control. My nutes have plenty, the plants are just currently unable to use them. Hope this helps. Maybe someone with more experience will come along soon to help you out.