[kkthrowaway]

i was checking my 20gal clearwater tank, and noticed with alarm that a couple chunks of red fin were missing from my betta fishes, cthulhu, tail. i moved him in about two weeks ago, and he now lives with 10 ember tetras.
ive noticed that he is making these abnormally sharp turn arounds, as though he were quickly looking behind him. could this be him biting his tail?
i dont think it is fin rot, and my ember tetras arent fighters at all.
any tips? a photo is below.

 

[Mr. Limpet]

It's a double-tail betta, isn't it?

 

[kkthrowaway]

It's a double-tail betta, isn't it?

yes, he is.

 

[Mr. Limpet]

It looks like its fins are still growing out, & the new parts have less red pigmentation. I can't imagine a fish nipping its own fins.

Btw - great name for a betta!