Since you are inquiring about using magnesium as a supplement to help control seizures, I merged your post with this discussion, "Magnesium levels and epilepsy?" so you could read past posts on this topic and talk with members in this discussion like @ks835@dawn_giacabazi@jktaheri@robertjr and others. @jakedduck1 also may have some thoughts for you.
You also mentioned that you had tried modified Atkins in looking to try some holistic strategies/supplements that may be effective in treating a intractable seizure disorder. How did this diet work for your son?