My water parameters are (and I'm rounding up just to be safe) total ammonia-0.25 , toxic ammonia- 0.013, nitrate-40, nitrite-0.5, pH-8.0 He is in isolation, though, without the benefit of the biological filter. I used to have him in the main tank (he gets along beautifully with the other inhabitants, in case you were wondering), and ammonia levels in there are un-detectable.
I used to do water changes every few days because I was treating the tank for ich. The betta and some other fish were itching. Since I stopped the treatments, I've gone almost two weeks without a change. I figured that constantly fluctuating water was stressful for them, too. But everyone looks real good.
I've had the betta for 2 and a half months. His fins are a little scraggly at the edges, but other than that he looks perfect. Actually, the swelling on his stomach is almost gone, his vent area is only slightly swollen, so I'm guessing those are normal and I just never noticed them before.
In terms of behavior, he's acting absolutely normal and healthy. He doesn't seem to be suffering from any physical discomfort. He actually puts up with my recent use of spotlights to examine him closely without even swimming away. So he's not shy or afraid of me.
This morning I gave him a few flakes, soaked so they would sink. He was STILL picky, can you believe it?! He did his usual routine of examining it suspiciously, trying a piece and spitting it back out. After nearly a week he's still finicky. The only food he really goes for are his pellets (which do sink, as well, if presoaked) and worms. So that may be my only route. He has me trained.
Oh, wait! I remembered that he DOES eat food he normally rejects if the other fish are going after it. He was getting his special ration of pellets while he was also eating flakes meant for everyone else. That would explain the swollen belly. He was just overeating!
Well, I think this case is closed. I'll write another post if any other problems arise, of course. Thanks for your responses. Please do answer this one if you have any suggestions about water quality/water-chanting.