As for going with metal halides, I wouldn't second guess it, you won't need a chiller, I'm running 2 400 watt 20,000k halides and 1 150 watt 20,000k halide on my 180 reef, with a completely closed in canopy and two 4" computer fans, I do leave the lid up on my canopy about 1" to help vent, my temp only gets up to 78 during the day and back to 75.5 at night.