I have no idea what caused it. He was fine and a few days ago he was having swim bladder issues so I fasted him and I offered food only for him to ignore it. He had no interest in food and I noticed pineconing. He was fed bug bites, pellets and frozen blood worms. He wasn’t sick up until a few days ago, normally was an active betta that begged for food.
i did test the water. Ammonia 0ppm nitrite 0ppm and nitrate 20 ppm