I purchased a 13 watt upgrade kit (including reflector, ballast, etc) from www.ahsupply.com to upgrade my eclipse 6 gallon. It's great, lots more light and my red plants are actually turning red now. Now, if I could just get that dang DIY CO2 working right

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How much light does the eclipse 12 come stock with? You could probably fit 2 12 watt bulbs under that hood, you may have to leave off the reflectors depending on size though. I actually could have put two of them on mine, but I chose not to because I don't need THAT much light.
Here's instructions for setting up the eclipse 6 gallon as a nano-reef, I think it could be easily followed to change the 12 gallon to have more light. Hope this helps!
<a href="http
/www.turetsky.org/nanoreef/" target="_blank">http
/www.turetsky.org/nanoreef/</a>
EDIT: I just saw where your post says how much light you have. I'd either get two of them or try to leave your stock light there and add another one, depending on room.
Oh, and it's important to remember that if you do this you'll loose the ability to use that nifty on/off button on your hood.