I have some Heterandria Formosa fry in my tank that appear to be, umm... sinking, is probably the best word for it. I know that (at least i'm pretty sure) that fish have to have a first breath of air, but these fish have been swimming around for a couple of days now. But today when I got home, I noticed that a few of them were having trouble staying off the bottom, They could struggle to the top, but then they would just sink back down. I have a thin layer of surface film that I don't know how to get rid of, but it was never a problem in the past. Also, the adults are doing fine and eating well.