Betty's tail is totally shredded in the course of a day?

[Tanlefan]

I got home from work and Gucci's tail is completely shredded? It was 100% fine last night, and I'm pretty sure I would have noticed something wrong this morning when I fed him.  He's in a 10 gallon with a handful of ramshorn snails and a few dwarf emerald rasboras, who have never shown the slightest inclination to nip his fins.

I did dose the tank with the med trio in my initial panic, but I have had bettas in the past and I've never seen this sort of fin damage done in the span of a day. What could have caused it?

[FrozenFins]

Emerald Rasboras can be fin nippers, I would try aquarium salt and it should help