I'm pretty sure that is tail biting. Doing daily water changes can actually cure this since it looks un-severe. It can heal on it's own is what I'm trying to say. Good luck.

 

^+1

 

There's no real cure for fin-biting nor has any definitive reason been established. As suggested, warm and clean water will help prevent secondary problems such as fin rot but only time will tell if he stops or continues. I don't think daily water changes are really necessary, however.

Biting is the bane of owners who have Betta with such long, lovely fins. Sometimes they figure out it's easier to swim and maneuver with a shorter caudal. :-(

I do question: Since there aren't really "chunks" removed, is there any ornament in there which could be splitting his caudal?

 

Actually it's not fin biting, the chunks are not U shapes and are not wide enough for the mouth. It's definitely from some sort of decor or hard silk plant in there. But treatment is the same, just keep the water warm and healthy as already stated

 

That's what I was thinking; doesn't really look like biting to me, either.

 

Hmmmmmmm his decor is 2 silk plants that are as silky as a silk plant can get, he has a sponge filter, a Betta leaf hammock, the only questionable decor I think he has is his yellow petco flower ball cave... Could that be causing it?

 

If you take a piece of pantyhose and run it over the cave and it would rip it can damage their fins in the same way.

 

Silk plants are not always as safe as everyone thinks. there are sharp edges on the plastic stem parts.

 

It could be from the betta leaf hammock. In my experience they seem a bit sharp.

 

Yeah I agree on the hammock. And for the silk, generally the stems aren't the issue, some silk/fabric plants the leaves can be really stiff which makes it easy to tear a tail on the leaf. I actually got a paper cut from one once >.< I felt really dumb about it lol but it wasn't the typical silky leaf like they normally are which annoyed me since I really loved the look of the plant (It was based of Lobelia Cardinalis so it was really beautiful). Anway, I'm not sure about the cave, I think that should be good but if it's resin you can take sandpaper to the sharper parts if you feel like that's the cause and see how that does.