Howdy. You asked me about one of my tanks with a grassy bottom. That was Dwarf Sags, Saggitaria subulata. That will lawn out under pretty low light (though it grows taller in lower light). I have managed to put a lawn of it in a 5.5 under a single 12 watt bulb, and a good thick mat of it in a 10 under a single 23 watt spiral compact about a foot over the tank. Really good and easy plant.