long tail betta are a troublesome bunch with tail damage.
I found this quote in another thread....
Ok, I'm relieved to hear that other people have random problems with long tail bettas. I have a male betta that's either a delta or a half moon. The LFS that I bought him at told me he was a half moon. Anyway, I went out of town over the weekend & when I came back, his fins were all torn up. :( How do you treat your betta's torn fins? I don't see any kind of black spots, so I don't think it's fin rot. His color looks a little bit less vibrant, but that could be because he's under a different kind of light. He has an incandescent light in his tank now as opposed to the LEDs he had in his 3gallon. Help! :(