On a 55g, i would use a 2 bulb t5 fixture, one bulb around 6500k and the other 10,000k. If you want a heavily planted tank, you will want to look into adding a source of CO2, as well as the basical nutrients that planks need: nitrogen, phosphorous, and potassium. Seachem Flourish is a good fertilizer that gives plants sufficient nutrients. I have made a DIY CO2 system before and i have used the Seachem Flourish Excell. Both ways of CO2 entry worked fine and produced great results.