Swim bladder treatment

I recently bought a betta that seemed to be struggling with swim bladder. He seems to be getting better after his first day home. He is able to swim around but his body sometimes looks like it’s curving down? And around 15 seconds or so he will stop and his body will sink and he’ll fall on his side. I put my tanks water to 1/3 of the original hight leaving about 6 inches of water. I’ve also been fasting him for about 2 days.

My main question is, is it normal for bettas with swim bladder to not have a bloated stomach? His stomach looks normal and besides his occasional resting he is very energetic. He’ll come greet me when I walk up and has been investigating around the tank. I’m worried that his stomach not being bloated means it’s bacterial swim bladder rather than just gastrointestinal.