40 watt isnt enough. Its way too low. The guideline is 2-3 watts/gallon. Here is a cheap method(your lucky you have a 55 gallon) to replace your current lighting for cheap, should not cost above $70.
1.Return your hood, and the light bulb and get a refund.
2.Go to home depot, and get shoplite fixtures that can hold two 40 watt ,48inches ,T12(T8 is slightly better) bulbs,then get two of these(choose the one that fits your tank). This should cost around 15$ each
3. Buy bulbs(at homedepot, too!) labelled as daylight,super daylight. Get 4 of these at about 40watt each. each bulb cost approximately 5-10$. Try to mix and match bulbs from different companies, too. Dont buy ultra exensive bulbs at the petshoppe! Unless you feel they are better and have money(if you do have money, consider power compacts).
Thats it. This should give you enough light to grow almost any plant, even some red ones.
Also, you might wanna think injecting co2, as this does wonders to your plants! And btw, whats your substrate.
Hope this helps, and some great people around here can also help you more.