Light hood rebuild... I need some advice

[dow]

I've got a 65 g tank that I've had set up for about two years or so. Before that I had a 40 breeder (same footprint) for about three years. With the 40 breeder, I set up a light hood that housed a single 175MH lamp, which was great for the 40 breeder. The hood is designed so that the lamp is about 9" above the water and is enclosed except for a gap in the back that is 4" tall and runs the length of the hood. When I moved to the 65, I didn't make any changes to the lighting due to money issues and because I really didn't need the additional light for mushrooms, polyps and fish. However, the 65 came with glass cross brace that's about 5" wide or so, and is directly below the middle of the lamp. Here's a diagram of the original setup:

http://www.flintrockdesigns.com/images/images/hood-original.gif

Well, I recently upgraded my lighting from the single 175 to a dual 250 MH setup. I did the upgrade for a couple of reasons. 1. I'd like to move from mushrooms to stonies; 2, I'm trying to get away from having the center brace block part of my light; and 3. I got a great deal on two ARO 250w electronic ballasts (I already had the second mogul socket and reflector). The current setup looks like this:

http://www.flintrockdesigns.com/images/images/hood-current.gif

With the new lighting, the tank looks great. However, heat is an issue. I've added one of the larger Radio Shack 110v fans to the back and it's blowing air into the hood, which is causing air to circulate in and then back out the back, but it's not helping enough. In order to keep the tank within an acceptable temp. range, I've had to cut back to running one light at a time.

I've got a few options that I"m considering, and would like your advice and recommendations on them. I'd like to stick with the same hood (with some modifications) if possible. Here's what I've come up with so far:

1. drill some vent holes in the top to give the heat a place to go and possibly add a second fan to the back;

2. Drill a hole in the end of the hood and install the fan there, with possibly a second fan at the other end to push air through the hood;

3. Make the modifications in #2, and re arrange the lamps in this format, so that the air is running along the lamps from one end to the other:

http://www.flintrockdesigns.com/images/images/hood-proposed.gif

As much as I'd like to go with a pendant design, that isn't really practical in this case sine the ceiling is about 16 feet up here, and I don't think that my wife would bee too gung-ho on having wires hanging from the ceiling down that far.

Any thoughts or ideas that you might have would be great.

Thanks,
Dow

[ej1698]

I WOULD GO WITH #2

[SuperAWE]

Yeah #2 with two fans in a push/pull combo. You may want to try flipping your reflectors around for the airflow, dependnant on how the new lighitng looks.

There are a load of super quiet fans out there, best to go with as large as possible with slower rpm..maybe 120mm's versus smaller and higher rpm.

[RumLad]

Drill a few holes in the cabinet, have the fans at each end pulling air out of the unit. I have heard that pushing air into the cabinet is not a good idea as it lowers the life of the MH bulbs.

[miwoodar]

I have a 65 with two 250 MHs and two 95 watt VHOs. I have one 30 cfm computer fan pushing in from the back. The top above the reflectors was left open. I even sealed the back of my canopy with foam board insulation to force all air to go past the halides and out the top rather than the back.

I initially had one fan in, one fan out. The one facing out died a very early death due to the humidity. It didn't cool the tank as well either.

I've heard mixed thoughts on halide bulb temps. I don't have my fan pointing directly at my bulbs.

My camera is dead right now or I would take a pic.

[kgross]

Put 2 fans on the canopy, one on each end with the both pushing in. Have the back open or lots of holes in the top to allow the hot humid air out of the system.

Kim