I did that but the mounting brackets only raised the fixture a few inches above the tank plus I can't have a hood on the tank because the mounting brackets are in the way. I don't want my piranha to jump out!
Get a rheostat from home depot or lowes.
http://www.homedepot.com/Electrical...splay?catalogId=10053&langId=-1&storeId=10051
I use these to control the heat mat for my reptiles, works great.