Hello! I have one flame dwarf gourami in a 15-gallon tank with three platys and five ADFs. Today, the gourami seems to be gasping for air. He is moving around fine, not staying at the top or the bottom or anything, just opening and closing his mouth quite rapidly. I know this can be a sign of poor water quality, but everyone else in the tank is completely fine and my parameters are good. He has plenty of hiding spots and the tank is not overstocked by any means, so I don't see why he would be very stressed, but that's the only thing I can think of being wrong. He doesn't seem sick at all and his physical appearance is just fine. Any ideas?