Planted Tank Enthusiast
Join Date: Aug 2007
Location: Catonsville, Maryland USA
Based on my experience, I suspect that may not be enough light for what you want to do. But knowing what type of light fixture you have would make it easier to answer your question. Watts per gallon is a rather imprecise method of determining lighting intensity, and doesn't really work on a tank that small.
My daughter's 5.5 gallon shrimp tank has one of those fixtures meant to use tubular incandescent bulbs, and I substituted a coralife 10 watt compact fluorescent bulb. I would consider this to be low light. It works well enough to grow Hemianthus glomeratus, Myriophyllum mattogrossense, Rotala rotundiafolia, and Lysimachia nummularia. No co2, weekly dosing of Flourish after water changes. Growth is slow, but it looks pretty good.
If I were setting up a 5.5 gallon high tech tank, I'd use fixtures like the ones on my 2.5 gallon tanks. (The tanks linked in my signature) They are power compact fixtures with 2 13 watt bulbs. I use diy co2 on those tanks.
As the previous poster stated, co2 is always beneficial, even without high light.