I've had bad luck with my bettas recently. I had two males in a divided 10 gallon and 7 females in a 55 gallon community tank.
But a few months ago one of my male bettas developed swim bladder disorder. I put him in QT and treated him first with epsom salt and when that didn't work I followed the advice of some on here and tried two different antibiotics, and they didn't work. I felt so bad for him because he just sat on the bottom all day and had a really hard time coming up for food. Then last week he died. I was kind of relieved, though, because it made me so sad to see him suffer and sit around all day doing nothing.
Then one of my females in the sorority got dropsy and died less than a week later.
Then... I'm such an idiot... One of my females was being a super bully so I put her in time-out, floating in her cup in the tank. It had been about a week and I was about to let her out again but later that day I noticed her in the cup just hovering vertical. And I was like "ooohhhh craaap". Something happened and the cup tipped over and water came in completely filling up the cup to the lid so she couldn't breathe and she died. I felt the most horrible about that one because it was my fault.
And then I thought one of my other females was dying the other day because she was completely clamped up and not moving. Her gills weren't moving either a few times when I looked at her, so I thought she was dead. So to make sure she was, I jiggled the cup and she woke up and started breathing again. There were like 3 times when I thought she was dead. I put her in her own 1 gallon and within about 24 hours she's almost back to normal, swimming around and eating. She's a little clamped still but not as much as before. So that one is a success story. But when I thought she was dying I was just like, "Uggghhh 3 bettas already died on me in the past month. Not another!!!" So I'm glad to see her back to normal for the most part.