I did the same thing...got a 30W bulb with my aquarium purchase, and thought I could get a better higher watt light for it. Unfortunately, I found that you can really only change the color spectrum, not the wattage. I found that a bluer light, for instance 50/50 actinic/daylight bulb is much more beautiful, but will not support corraline algae or corals. Then I did a little more research and ended up with an Orbit 192W lighting system that set me back another couple hundred bucks...my aquarium looks great, but I am still paying it off!!!
At least I filled in the money pit...after the initial setup, maintenance only costs a few dollars a month.
38 Gallon (Freshwater): 1 Green Swordtail, 3 Yo-Yo Loaches, 1 Clown Pleco, 1 Blue Gourami, 4 Otocinclus, 7 Cherry Barbs.
46 Gallon (Saltwater): 60 pounds Lalo Live Rock, 60 pounds aragonite sand, 1 Coral Beauty Angelfish, 1 Peppermint Shrimp, 1 Mushroom Coral, 1 Emerald Crab, various snails and hermit crabs.
10 Gallon (Saltwater quarantine):