When I was a kid I had 8 tanks in going in the basement. One was just a 5 gallon tank with an incandesent light over it and several fronds of Water Sprite. Since it wasn't rooted it floated. For some reason the conditions were conducive to growth and the fronds became decent sized plants that grew right out of water. It also covered the surface, so it also prevented light and algae beneath them. It was also great for refuge. I had spawned a pair of Bettas in there and long since removed the fish. 6 months down the road a spotted some movement. Well, one of the babies survived being in there, without filtration or food or any attention at all. I'm sure it also works for livebearers. Anyways, I've always been fond of Water Sprite. I also had good results from the plant bulbs, at least the one that has a flower that looks like pipe cleaner.