Could be body rot. I don't know much about it, though...

 

I don't know what could have caused it but you could try some Betta fix or Melafix and see if that helps him. Are your plants plastic? They can hurt themselves on plastic plants.

 

Thanks, I was wondering if it could be the plastic plant. Since I wrote the post I went to Petsmart and they suggested Quick Cure, a total water change and putting him into a new container. Today I put him into an new 1 gallon vase with no stones or plants and 1 drop of Quick Cure. I will write a post again in a week to let you know his progress.

 

Sounds good. Good luck with your fish.

 

You might want to look into having a bigger tank for him to actually live in like a 2.5 gallon or something. Makes water changes easier (you can do partial changes instead of full) and even that little bit of a bigger size keeps the tank a little more stable than a 1-1.5 gallon will. Do you use a heater with him?

Also, instead of plastic plants they sell silk ones that I really like to use with everyone, not just just my bettas...those won't hurt your betta and you might find him sleeping or resting in them