I've been having some challenges with Jack lately. I switched his tank with my other betta Mo for various reasons that I won't go into. Prior to that, Jack had somehow torn his caudal fin. I took out the only decoration that I thought could have done it. After switching him with my other betta however, I came home today to find that he had managed to shred his dorsal fin. >_<
Mo lived in that tank for 4+ months without a single incident involving his fins. I have come to the conclusion that Jack must simply want to be a crown tail... because that's sort of what he looks like now.
In any case... my avatar is a pic of him prior to tearing up his fins. I might post an "after" image later.