I'm seeing lots of good advice here, but I thought I'd chime in a little.
Plants will grow fine with a bulb in the 5000-7000K spectrum. ~6500K is ideal, yes, but you won't have magically better results going from a 5500K to a 6500K bulb.
I really recommend reading over Byron's four part guide for plants, it is full of information you may find useful, and also stop by the plant section on the forums here. Lots of helpful people.
You have Water Sprite, which can be grown floating and is actually very good at it. Floating plants provide excellent shade for the fish below, and most fish thrive under the cover of them. Fish do need rest, and do need periods of absolute darkness each day. Bright lighting, as you've seen, is stressful to these fish. Most tropical fish come from forests and marshes where there is a thick canopy of trees providing shade, they are not exposed to direct sunlight all day.
Are you using a fertilizer? A comprehensive fertilizer like Flourish is ideal as it provides all the nutrients plants require in the correct proportions with the exception of light and CO2. Your fish and decaying mater will provide all the CO2 you need, and your lamp will provide the light. The photo period (the time the lights are on) should be kept under 12 hours a day.
Plants will photosynthesis all out until they run out of a nutrient they need. Once they run out of a single nutrient, they stop. You really want your light to be the limiting factor, because otherwise algae will take advantage. With light being the limiting factor, algae does not stand much of a chance as the plants will out compete it for nutrients. There will always be some, and a little is good, but it will never explode if you limit your light (either by intensity or duration).
The lamp you currently have is more than sufficient for a 5g aquarium. How old is the bulb? Fluorescent bulbs only maintain their full spectrum intensity for about 1 year, after which they need replaced. Your eyes won't notice a difference, but the plants will. The 'angel' won't mater, straight down is fine. The distance from the surface however does, the closer it is the more intense it will be for the plants.
You may consider getting a fixture that uses are regular spiral CFL and use a 10W 6500K bulb. That could safely be placed directly over the tank and provide a moderate light level.