Magnesium levels

I keep asking my sons neurologist about low magnesium associated with his seizures.i just read on this site that low magnesium can cause abnormal electrical activity in brain cells. My son had normal MRI and abnormal EEG showing a small area of abnormal electrical "sparks". his blood work showed a magnesium imbalance. Every time I mention this to the dr he says  that wouldn't show on an EEG,which may be true,but the low magnesium could be his trigger. I'm feeling fustrated as I would like to pin point my sons trigger.