A couple of questions for you:
1) Is there a reason you're using pH up?
2) What's the pH of your tap water?
Betas do well in slightly acidic water, so I'm wondering if there's a reason you're increasing the pH.
Also, very importantly from the perspective of treating fin rot:
At lower pH, there will be more ammonium (NH4+) in the water. This is OK. Conditioners such as Prime work by temporarily converting ammonia (harmful) to ammonium (safe). A lot of people add tannin sources, such as Indiam Almond Leaves (IAL) or oak leaves, because they acidify the water slightly.
However, at higher pH, these wastes convert to ammonia (NH3). This is not OK, as it can contribute to conditions like fin rot.
So my suggestion would be to keep the pH in the neutral to slightly acidic range.
3) What brand of food do you feed him?
4) How much do you feed him each day (or each time)?
A Betta's stomach is about the size of his eye. So it's easy to overfeed them. I count out pellets, and then feed them one at a time to my guys. It allows me to monitor exactly how much they get each time.
If he's bloated from being overfed, you can simply fast him for a day or two, and he should be fine.
Also, take a look at the ingredients in the food. Foods that contains a lot of grains or fillers can contribute to bloating and constipation. (For example: wheat, corn, soybean, gluten, etc.) If the food you're giving him contains a lot of these, consider switching to a high protein based pellet. (There are two brands that people on this forum often recommend: New Life Spectrum Betta pellets, and Omega One Betta Buffet pellets. But there are other quality brands too.)
Last edited by LittleBlueFishlets; 07-02-2013 at 12:38 PM.