My Red Devil is 13 years old and over 12" in length. I understand that the tank it has always been in is too small at 29 gallons but he has done well till now. He is quite listless, and stays on the top of the tank near the filter. I do not see it gulping air at the top and when I tried feeding it this afternoon, it ate the food and within a few minutes spit it all out. I did a 50% water change with no immediate results. I also just added some Melafix. The only problem I ever had with this fish was a buoyancy (air bladder) issue a year ago which was resolved after a similar treatment of numerous water changes and one melafix treatment. The fins and color all look fine. Any feedback would be greatly appreciated.