36 x 36 is a very large tank. I've seen a reefer do a single 250 watt MH on a 32 x 32 size tank, but it was single ended bulb in a 20 inch square reflector. I think he felt that he was pushing the limit of his light spread with this set up at 32 inches. I think it's possible, but you'll need to make sure that all of your rock is directly in the middle of the tank with probably 6 inches of space between the rock and the glass on each side of it. This would give you 24 inches of rock to cover with a single bulb which would be about right. You'll need to choose your bulbs wisely and only use high PAR bulbs to get the most out of it.