When the MHs go off, the light on the fuge goes on. It helps avoid that night time dip in pH to run it like that.
Ahh ok...gotcha. Now to create a reef that gets the Grins stamp of approval! LOL
For zoos, you definitely don't need that much light. Your tank is pretty short, too.
You obviously have some skills in 'DIY', so you really could/should go that route.
For example:
http://www.championlighting.com/product.php?productid=900032&cat=768&page=1
That's a dual 150 watt HQI ballast for $65.
Look around and find a good deal on some bulbs and pendants, or reflectors and sockets, and you could have your full metal halide system for under $200 (with shipping and stuff).
Even a few 175s would be enough light.
And, since you do want to do mainly zoos, actinic support is in order. Get a vho or t5 or even cf setup and call it good.
Anyway, rambling advice main point: Build yourself a hood and DIY your lights...
Would 1 250w MH DE and 2 96w CF actinics be enough?