For an alternate suggestion...
Personally, for cheap lighting on a 5.5g (rectangle AGA tank, I'm guessing), I'd do a DIY 15" 14w NO flourescent job. One bulb would be good for low to mid light plants, 2 would be great for higher light plants. Lowe's carries a 2x20w electronic ballast that would work, then you would just need some end sockets and bulbs. I'd do GE Plant & Aquarium bulb, or if using 2x, one of those combined with another bulb if the coloration isn't good for ya.