I've been trying to research the problem I'm having with my betta, but no luck yet.

My little blue betta, Squishy, lives is a 2.5 gallon tank (it's a custom tank that sits inside a gutted out iMac). He has a heater, filter, and gets 25% water changes every two weeks (though since he's been sick, I've been doing it every few days). He was getting tap water with Start Right, but now I've switched to Spring Water.

About a month ago, I noticed a "bulge" on the side of my little betta. It's fairly big compared to the size of my betta (he's always been a little guy). It almost looks as if it's filled with air or clear fluid. He's eating fine, but not as active as usual, and is spending a lot of time at the bottom of the tank, which he never used to do.

I stopped feeding him the freeze-dried food. I did a whole tank change and used the Fungus Clear tabs in case he had fungus, but that didn't help. I took him to the pet store where I got him, and they thought he might have a parasite, and gave me some Pepso Food to try. He will eat it, but is still not better. I also tried Aquarisol. No luck. After a water change, I tried Betta Cure for Ick & Parasites. Still nothing. He is eating, but again, is just not his regular perky self. He seems to have a hard time swimming around (not surprising, being that he has a giant growth). I don't think it's dropsy, as his scales seem okay.

Any ideas/suggestions?

thanks!