Hello again. I copied and pasted bettababy's response to my problem below. Like you said though, your pics look different than mine. I'm not sure if it would be the same thing or not, but this is what she said. I did everything she said below and the swelling went away. However, now that he's been back in his regular water for the last week, he seems to be swelling up again. I've talked with her and decided to do another round of medicated water. I'm estimating, but I would say it was about 2 weeks he was swelling before I started treatment. Then that was another 10 days and he's been back in regular water for about a week and a half. So he's been sick for a month or a little longer. Bettababy has had a lot of "non-fish" related things going on, so it may take her some time to get back with you. I don't want to recommend you doing the below treatments b/c I have no idea, but she does say that they are safe and won't hurt the fish. Even if your problem is different than mine, it may not hurt your fish to try them. It's at least a place to start. I hope this helps.
There are 3 things that commonly cause swelling like that in the stomach area.
1. dropsy
2. Internal parasite/worms
3. Internal bacterial infection.
With dropsy the scales will stand up and the appearance resembles a pinecone... and I don't see that happening in these photos.
Based on your information, it could be either of the other two.
Via internet there is no way for me to diagnose between parasite and bacterial infection, that's the bad news. (I would need a feces sample to put under the microscope to identify the problem) The good news is that I can suggest the proper meds to treat for both, it's safe, and which should effectively take care of either problem.
Please be very specific on these medications, there are no substitutes, and if you mix certain meds they can be toxic.
The first medication is called metronidazole. It's a white powder and should be pretty easy to find. This med is going to coat his food for 7 days.
Take a small amount of his food (enough for 7 days) and put it into a zip lock baggie. Add a very small amount of the metronidazole to this, zip it up and shake it until the medication seems to disappear. In between feedings (once/day) keep the bag sealed and in a cool, dry place. It's important not to feed more than a bit or 2 at a time to be sure he's eating it right away when it hits the water. If this means making his meal time later in the day so he's real hungry, then that is fine... but he needs to eat the food before the meds leech into the water.
That should handle any problem he has with internal parasites/worms. DO NOT feed him any more peas. If the peas happen to cause damage, which is very possible... that could complicate things and cause a treatable illness to be fatal.
Next you'll need to get Fungus Eliminator and methylene blue. Do not substitute the fungus eliminator with another medication. If you can't find it I can find you a link to purchase it online. Fungus eliminator has very specific ingredients that are not found in any other medication available as of this time, and I have not yet been able to replicate each one in a proper dose to prove as effective and safe as the actual medication available on the market.
Dose both the methylene blue and fungus eliminator into a bucket (bucket should have a cover) of clean water (after treating with water conditioner). (Please be forewarned that these medications may stain acrylic, so if it's possible to put him into a glass hospital tank, that is always best). Follow dosing instructions for each medication as instructed on the bottles. DO NOT OVERDOSE.
The first water change should be 100% in the medicated water. Remove all carbon from any filter that may be running, but I find that stopping a filter during this treatment proves more effective. Each day for 10 days, do a 50% - 100% water change with the medicated water in the bucket. Once the meds are mixed into the bucket of water they are good for 2 water changes, then need to be mixed fresh again. Because of the dosing instructions, it is often easier to mix a 5 gallon bucket at a time. If you are doing 100% water changes daily, you should be able to use most of the water, so there should be very little waste. To dose directly to the tank is not suggested.
If he is going into a quarantine tank for treatment, break down his tank, clean everything well with running water, and start things over. It is safe to use bleach water provided you rinse extremely well, twice, and let everything air dry for 48 - 72 hrs. If the meds are going right into his tank, then sterilizing it won't be needed.
At the end of the 10 days, do another 100% water change with unmedicated water, and keep a close watch over him. You should notice the swelling starting to go down within the first 7 days. If after 12 days there has been no change in his condition, please let me know. I have every confidence in these meds, they are quite potent, while still being safe.
Raise his water temp to 80 - 82 degrees.
Please remember that not all meds are safe for a betta, and not all meds are safely mixed, so please don't try experimenting with other meds without some kind of professional advice.