I had 1x 400 Watt, 1x175 Watt MH's + 2x96 Watt URI VHO actinics over a 36"x18"x18" tank. I ran two fans one blowing inside the hood other one outside. I didn't have a chiller and didn't have any heat isues. If you use a Luminarc reflector probably one 400 Watter will be good for 24"-30" but if your tank is longer and wider you may need other bulbs.
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