Actually, the 18,000k PowerGlo bulb will support freshwater plant growth just fine (it's one of the few exceptions outside of the "ideal" kelvin range for flourescent bulbs). I think you may actually like it quite a bit if you run just one of the 18k paired with one of the 6500k in your fixture- that's actually one of my personal favorite bulb combos in terms of color rendition/visual appearance in a planted tank. 
Your light fixture should be fine for a low light/low tech setup. Stick with some of the hardier plants (check out the list stickied at the top of the Low Tech forum).
Your light fixture should be fine for a low light/low tech setup. Stick with some of the hardier plants (check out the list stickied at the top of the Low Tech forum).
