I have a 10 gallon tank, with 5 tiger barbs and 3 green tiger barbs. They have lived together in harmony for a while. Today, after my 25% partial water change, I noticed that one of the green tiger barbs was losing color - he's a dull, light green color now. And he's swimming sort of listlessly behind the others. My barbs are pretty playful, and like to nip at each other, I'm afraid him becoming listless will cause his eventually nipping to death. Anyone know what is wrong? My pH is 7.2, and everything else seems to be ok. None of hte other fish seem to be experiencing any distress. Thanks.