Zebra Barred Dartfish - Conspecific aggression

[PotatoPig]

I’ve had two of these fish for a while now, and they’ve gotten along great. They always hang out together, hide out together and share a burrow together. Until today.

One of them (slightly larger of the two) is very suddenly out for blood.

Has anyone whose had these fish experienced them being aggressive to, well, anything let along each other?

 

[blaxsun]

I had four which paired off into two groups. One pair eventually chased the other two out of the tank.