magnesium/natural calm question
 

I just received my Kid's Calm (natural orange) and have a question on the dose. My son currently takes 300mg. Magnesium Chelate. He weighs 89# and is 8 years old. I am confused on the supplement facts because it states that 1/2 t. has 85mg. Magnesium citrate and then for Vitamin C it has 200mg (as magnesium ascorbate). So does that mean he would be gettin 285mg. magnesium in a 1/2 t. or just 85mg? I don't understand the Vitamin C as magnesium ascorbate. I am assuming that I should keep him on a similar dose to what he has been taking. Also, since magnesium citrate is more of a laxative, will I need to cut back for that reason. The only reason I am changing is to try to decrease his number of pills. He has a tic disorder and I currently have him on 300mg. magnesium chelate, 500mg taurine, 500mg Inositol, 100mg B6, 500mg calcium chew and 20mg zinc. He is also on Gabapentin. It seems to help his tics. He takes an epsom salt bath twice a week. If anyone has any recommendations for me so I can reduce the number of pills he is taking, I would really appreciate it. I tried getting a combo mag/cal pill (Dr. Weils) but the pills were too big for him to swallow.
Thanks!