Sudden flaring & aggression from my betta towards Cory?

I've had a tank set up that's had guppies, a Cory, mystery snails & my betta who grew up with the other residents. The betta moved in with them as a tiny baby & there were no issues. The guppies passed away over time, & everyone else has been peacefully living together for 2 years, but today there was flaring & aggression towards the Cory. Any idea why?

 

My thought is that with the change in residents, the betta has become bored but more importantly, that a betta's aggression is hormone, rather than character driven. He can't help his aggression - whether triggered by
maturity, the resident change, boredom or annoyance at this other animal being in his territory. He'll view that tank as 'his' whether he grew up with the cory or not & territory disputes are solved by betta with auto-aggression.

There are a few ways to try to reduce the two encountering one another but they kind of depend on the size & conditions of the tank.

Decor & plants can be moved around to change territories, more hides introduced for the cory, floating plants introduced for the betta or live prey like shrimp & pest snails can be housed for the betta to hunt.

Is this a tank you're wanting to retire? If not, I'd suggest that cory are social animals that typically live in groups of 5 or more, in tanks of around 20 gallons. Perhaps you'd want to increase your number of corys & separate your betta into a solo 5g or bigger tank.

I suggest this also because I'm currently treating a betta that had lived peacefully with his herd of corys for some time until he engaged in an unexpected aggressive strike. He was stung by a cory in that tussle & despite treatment, the toxin is having longer-term negative effects that I fear he may not survive. I'd hate for your betta to suffer the same as mine is, just because he's bred for aggression & one day it revealed itself. I regret following advice that cory & betta can be safely housed together. Perhaps separation is best.

Hope it helps & if you have other questions, you ask them. Lots of helpful tank keepers here!

 

Thank you for the response, perhaps he has grown bored after his other tank mates died. I considered changing the tank, adding more plants, & hides. I also have breeder nets so I considered using that as an emergency solution until I can sort out rehousing. I have a 5 gallon I can set up, but I need to cycle it of course before moving him.

 

Thank you for the response, perhaps he has grown bored after his other tank mates died. I considered changing the tank, adding more plants, & hides. I also have breeder nets so I considered using that as an emergency solution until I can sort out rehousing. I have a 5 gallon I can set up, but I need to cycle it of course before moving him.

Wish I had different solutions for you! If you go with the 5g, you may be able to kinda 'insta cycle' using filter media from the original tank. Good luck with him.

 

They're both well, I don't know what happened with them exactly. But both happy fish living with snails now.