do you have a hood at all on the tank? on every 55g ive seen the center brace sits flush with the top and the light or hoods fit right in, or over the brace. I went nuts when I first started planting my tanks, and quantum is right. a wise forum contributor once told me many many moons ago (ill try to dig up the thread) that lighting and supplements was all about balance. High light with no co2 or supplements will fail strike, usually winding up in an algae problem. Low light with high supplements, same deal. I use low light levels (40 watts on my 110g, 30 watts on my 20L, and 36 watts on my 55g) and just a few supplements (ill have to get the name of the food he steered me towards when i get to my parents house tomorrow but i think its plant-gro) and i dose every 2nd or 3rd day with the maintenance dose of excel. Sure, some plants just dont do that well, and everything tends to grow nice and slow, But everything stays nice and green and healthy as long as im good about pruning, and plant feeding.
if you want really high light, you need supplement routine to match, and probably co2 to get the most out of it. Thats fine, but it gets costly and you pretty much need a lawn mower to keep everything cut back :P