Metal Halide Cooling

I am setting up a 2x250 watt % 2x54 watt T5 retro kit under my canopy (90g tank with 38g sump). I took off the top and just framed it in to old the T5 pendents and the 2 T5 so it is very open. Also there is no back.
I wanted to see what size fans I should get and how many? My friend who I got this from used 3 4" fans on top. 2 pointing down pushing the air into the water and facing up pulling the hot air out.
Does anyone have a set up they like more?
I have 4 3" fans 80mm in a box already and wanted to use those, but I don't want to get into a heat issue.

Thanks for any help!

John

 

I've got the same lighting on the same tank and use 2 three inch fans. They seem to be enough with my sump and fuge in my basement. The more the better though. I think four would work out well for you.

Will you have them running all the time or on a timer or controller? Mine are on only when the mh are on

 

I was planning on a timer to go off about 1 hour after my halides. Where do you have yours mounted?
Someone told me they could also be put on the sump?
It get cold here from Nov through March so I will not know how well they work until next sumer.