I keep the area at 75 Degrees. I have a portable A/C I keep on the ground level below the shelf to cool down the room. I also have an oscillating fan on the shelf with the plants to circulate the air and create wind.

Also, the bulbs are HPS, not metal halide.

It really can't be over-watering because of how dry I let them get between watering. I usually go several days.. I might even be underwatering like someone previously posted.