Equal amounts by volume of magnesium chloride (Magnesium Flakes) to distilled or spring water.
I've found the highest concentrated magnesium chloride flakes are the Life Flo brand. See my Health Products page for a link to the their website. You can buy any magnesium chloride flake brand you want, but I've just found theirs in the most concentrated in magnesium. If you buy their brand and follow my recipe, you will be making the same exact recipe that I give you at my clinic. Change the amounts to whatever size you want your batch to be, keeping the ratio the same. This is how I make it:
2 cups spring or distilled water
2 cups magnesium flakes
Heat water on the stove just until it is hot but not boiling. Add your flakes and stir until they dissolve. Once it has cooled, store in an airtight container.