Banggai Cardinalfish attacking another Banggai

Hey all, I have two Banggai Cardinalfish in my 30 gallon tank for about two years now.



I came home tonight to find the larger Banggai Cardinalfish attacking the smaller one to the point where it shread the smaller one's tail caudal fin. I've removed the larger one and placed him in a container for now since I don't have a hospital tank setup.



Any thoughts on the recent aggression? They've been fine all this time, up until tonight...:cry: