I went on vacation for a few days and my room mate was feeding my fish for me. When i got home i noticed one of my Acei was looking sluggish and sick. His colouring was fine and he didn't have any marks or anything on him. So i cleaned the tank and did a large water change and fished him out of the tank. By this time he was floating half upside down at the top of the tank. I moved him to a 10gal QT tank with some aqareum salt and waited. I wasn't sure what was wrong with him. Not a mark on him. Within about an hour he was totally fine. Completely happy and swimming around the tank. None of my other fish have gotten sick. i tested the water on my main tank and it is fine. I kept him in the QT for about a week then tried to put him back in the main tank. The second i put him back in he went belly up again so i grabbed him, put him back in the 10gal. Then about 20 minutes later he was totally fine and happy again. What gives? The only thing i could think of was stress but what do i do? I can keep him in the ten by himself forever! I even added a bunch more rock to my main tank to give more hiding places but he went belly up before he even got the chance to check it out! :-?