The way to maximize plant growth is to use CO2, preferably pressurized CO2, with the bubble rate as high as you can go without giving the fish any problems. One T5HO bulb, with a good reflector is more than enough light for a 55 gallon tank, but the Hagen GLO light doesn't have a really great reflector. With 2 bulbs, like you have, I suggest having the light about a foot above the top of the tank. Less than that is just asking for never ending problems with algae. Another option is to put a layer of fiberglass window screening between the light and the tank. That reduces the intensity by 40%, and would let you keep the 2 bulb light about 3-4 inches above the top of the tank.