I recently had my betta in his QT tank (about 1/16 gallon) for a good four weeks. I was consistently changing his water 3-4 times a week. Each change contained Epsom salt to treat what i thought was SBD. I have now put him into his 1.5 gallon tank and have fasted him for 2 days. He is now unable to swim to the bottom and is floating on his side at the top. He is not bloated because he has pooped and not eaten in 2 days.
His tank is about 77 degrees and has a heater. It has a rock/cave structure with a fake plant on it. I have heard that they may float due to oxygen deficiency in the water but i am at a standstill.