Cutecotton, looks like its a cabomba. They need lots of light, or else the leaves will just keep falling off until it dies. Just add some more light or replace for low light plant, HTH.
oh....well now you tell me no im just joking they seem to be doing aright acutally, i keep the light on a lot (i'ts in a hallway that won't get any naturla light) so i just leave the tank's light on whenever the sun's out to mimic natural sunlight sometimes it's on for almost 10 hours
told ya i'm not a plant person..
okay next, what's in THAT tank! (plantwise i mean)