Mh placement

How far off the surface of the water should I put a 150w mh of a tank that has a foot print of 19x12.5x12.5? I'm completely lost as I have leds now
 
9" for MH. If it was higher wattage, I'd say 12" in a standard reflector.
 
I'd place it high enough to get the coverage you want rather than concerning yourself with intensity, after all it is just a 150w halide.
 
Top