Got a dumb question-- how do you hook them up (computer fans) so they can be pluged in?The 4-fan unit only pull 38.56 CFM. He has "2 175 MH and 4 80 T5's" inside a hood. He'll need much more air flow than that. The 5" fan (120mm) I use can pull 74 CFM each, and they only cost $5-$8. Have a couple of those on each side of the hood would be perfect. One set for pushing and one set for pulling air out.
do you know if they have a adapter with multiple outlets?Here are some 5" ones. The thing that you want to pick is the noise level and the air flow. Some of them even have lighted LED color. lol.
Since you have plenty of room to put fans (unlike computer cases), you can pick a couple of more quiet ones instead of those that are much stronger and more noisy.
Newegg.com - Computer Hardware, Fans & Heatsinks, Case Fans, 120mm
What I would do is put 2-4 fans on each side ( depending on how wide your tank is). And have the one side blowing outside air into the hood, and the fans on the opposite side would be pulling air out of the hood. That way you have a constant circulation of outside air going through the hood.