Bettas: Tail-biting or fin rot? how to tell

[marsh]

When an otherwise healthy betta has some parts of his tail looking shredded or missing, what are the signs that help us know if he is self-mutiliating it vs. an outside infection causing the damage?

 

[Delapool]

For me I find that fin damage in any fish will be deep splits that appear over night and heal up pretty quickly over several days. The healing I think an important point. If it is not healing than could be an infection or an infection has set in on fin damage.

Fin rot I don't get a lot of it (really struggle to think back) but no healing and the tail fin had changed color and look on the edges with bits of fin missing.