I don't know if the subject was the best way to describe this problem, but I guess it's a start. First, some general tank info...
Tank Size: 5g (divided)
Water Changes: 50% 2x/week
Tankmate: Another male betta
Decorations: Silk Plants & a very thin layer of black gravel (just barely enough to cover the bottom)
Ok, onto the problem. Maybe a month or a month and a half ago I lost his Dante's former tankmate to suspected Dropsy. I isolated the sick betta immediately and did everything I could for him but to no avail. On the day that I was actually going to euthanize him he died, maybe he knew it was time. Anyways, shortly after that I noticed that Dante's one side bulged out. The bulge hasn't changed or grown at all and the other side is completely normal. He's eating normally, although he seems a bit "slower" lately than usual. He's always been a bit slow, like you have to show him where the food pellets are and sometimes he doesn't catch them on the first try, but lately he's been a little slower than before. I did add the new tankmate about 2 weeks after the other betta died, but the "new" betta had been in his own tank for 4-5 months with no disease or parasite problems.
Anyways, just wondering if anyone has any ideas as to what it could be. I will have had him for a year in August, so he's probably almost 2 years old. Besides this, I've never had any major problems with him. He had some mild fin rot when I got him, but that cleared up just by doing lots of water changes and using melafix. So anyways, any suggestions would be greatly appreciated. Thanks!