Betta mutilated overnight, HELP!!!

[fish_4_all]

My betta was fine yesterday and now almost all of his fins are gone! There are 2 neon tetras, and 5 cory cats in the tank.

Could one of them have eaten them off?

Is it more likely that the betta got into the AC HOB and got mutilated?

My corys , c. trilineatus are behaving like they are getting ready to spawn, will this make them aggressive? A female is cupping her fins and grabbing ahold of a male, I assume this is mating behavior. Are they capable of this kind of damage to a betta?

Bottom fin is completely gone with bloody points and the top fin looks like something tried to rip it off with bloody points in the spine where the fin attatches.

PLEASE HELP!

 

[fish_4_all]

Ph - 7.8
Nitrates - 10
Nitrites - 0
GH - 250
KH - 160
Ammonia - 0

Tested by LFS today just minutes after first post.

 

[rich311k]

I have never heard of a cory hurting anything. I would have to go with the filter theory myself.

Do you have somewhere to move him so he can be by himself?

 

[fish_4_all]

I can seperate him out and I have already moved him out the tank with the C. trilineatus. I didn't find any fin in the filter so I don't know if the filter thing does work but it still could.

It is confirmed that the cories are spawning, at least 2 of them are. Eggs are everywhere. Will be posting in breeding about my corys big day!