Hi RocketSeason,
I'm sure you know that ammonia and nitrites should be 0, and nitrates should be no higher than 40
ppm.
Ammonia should be considered high if it's .25 or higher. Also, can you get the temperature up to 80 degrees? It's only 2 degrees, but 78 degrees is the lowest temperature I would consider comfortable for a betta.
About the bloat -- is it swollen where the pectoral fins meet the body, like he had too much to eat? If so, he may be constipated. Do you feed skinned pea pieces once a week?
Or is the whole body very bloated, and do his scales stick out like a pinecone? Look at him from above -- do his scales stick out? If so, he has dropsy. This is caused when too much fluid accumulates in the body cavity. Dropsy isn't a disease itself, but a symptom of a disease, like organ or kidney failure. In this case, try some epsom salt to draw the excess water out. I did google searches for a starting dose, and mostly I found that you should start out with 1/8 teaspoon per 5 gallons, ranging to a teaspoon per 5 gallons. Start out with the smaller dose first, and work your way up if you need to. You can always add a bit more gradually, but you would do massive water changes to get the salt back out if you add too much.
Dropsy in general can be hard to treat, and is often fatal. I don't want to worry you, but start treatment immediately if you think it's dropsy -- make sure you start lowering the ammonia and try the salts to draw out the fluid. Epsom salt can be found at the drug or grocery store. Good luck!