I came home today, and one of my betta's ventrals looked kinda ragged. There weren't pieces missing though, it was just a lot more... I guess flexible than it normally is, and it looks thinner, like a few layers were taken off. He's acting fine, and his caudal is still growing back nicely from where he bit it. I did change the water last night, but I made sure that I had enough water conditioner, so I don't think that my tap water is burning it off or anything. Could he have injured it somehow? Is it fin rot? Could he have nomed it?
So far I'm not too concerned, but I'm keeping an eye on it.