In the process of building my stand/canopy for my 75 gallon plus 30 gallon sump. I have 250x2 MH pendants that I will be running along with a pair of T5 actinics eventually. Is there a recommended clearance distance between the water and the bottom of the pendant?(the glass shield) I currently have 6" from the the water to the bottom of my pendant. I'm trying to avoid running a chiller.