Help!

[rob4191]

I've had a betta community tank for 3 years now and it's been just fine. I've never seen any aggression from the betta and hid tankmates were just fine. However, when I woke up his fins were - extremely - nipped and he won't stop flaring and attempting to attack my cories (if he's not hiding in a tiki decoration I have)

When I started the tank I had backup quarantine tanks, but don't have some right now. I'm confused as to why my fish have had an overnight change of heart.

Oddly enough, my Neon Tetras (who nipped the fins, most likely) don't seem to be getting bullied by my betta. Will provide with anything you guys need if I can.

 

[Byron]

This is very common and shows why we do not consider male Bettas community fish. Sometimes what you describe occurs immediately, sometimes down the road. But you/we cannot change the inherent traits of any fish, and Bettas are especially feisty, and bred to increase this aggressive behaviour. And many small fish like neon tetras when placed in a small confinement (almost any tank is "small" to the fish) frequently decide to nip fins of sedate fish. These simply cannot be combined. Three years is quite a spell for this to show itself, it is usually sooner, within several months, but almost inevitable if the fish themselves are healthy and normal to begin with.

What has occurred here is a completely unnatural situation for all these fish. And that adds stress that you cannot see, and in time something has to give. You obviously need to remove the Betta as it will not last long. And if it takes a dislike to the cories, they will be stressed.

 

[NickAu]

if he's not hiding in a tiki decoration

If he is hiding he is stressed, A male Betta is or should be the master of his tank and as such has no reason to hide.
Can you post a photo of the tank and a close up of the fish please