One of those flexible rope light strips can be picked up dirt cheap. I've seen them for 5 bucks. Attach the light to your reflector, and you have a moonlight. OK, it's not the fancy blue color, its just a very dim light in the tank, but it works just fine. I call it a "nightlight".
They make blue LED ropelights. Infact the more I think about it, the more I thnk I'm going to buy a string on post Christmas sale for a couple of bucks and have moonlights.