[Matt Nace]

Your buld is most likely 15 watts at 18 inches. Not too much light there. I am guessing there isnt space for another light, unless you Do it yourself??? ..or have to spend money for a custom light kit.

So..going with what you have I found Anacharis hardy, and grows without much light. Java fern and moss do as well. I don't know what your LFS would carry.

Check this link, to see what your LFS , or whomever you are getting plants from carries to see if they require higher levels of lighting.
http://www.tropica.dk/plants.htm

IMO, it is easier to have some plants, then none.

I bought some Anacharis to line the back of one of my 55's. It kinda went nuts in 2 weeks. I am going to have to throw a few feet away or find someone to take it.