Hey Robb,
I am working on a similar project, for my 15 nano. Here is a thread from the nano board, converting the AQ500 into a nano's refugium. You should be able to use some of it for your purposes:
http://www.nano-reef.com/forums/show...ighlight=refug
Also KrackerG, one of the nano DIY guys, has several inexpensive MH convertions, 70w,150DE etc. eg:
http://www.nano-reef.com/forums/show...threadid=24893
I found some of the same info also on reefs.org, esp. using a Home depot pendant (Raven model ? about $30) conveted to 70w MH.
Good luck
