PJ Cardinals fighting

I have two PJ Cardinals in a 55 gal FOWLR. One of the Cardinals seems to be beating up the other and chasing him all around the tank. The weaker Cardinal has tattered fins and a bruised mouth now. I thought they were schooling fish. Is one just asserting his dominance? If that is the case I should be able to get 1 or 2 more and everything should be fine I think. That way he will not be concentrating on just the one.



Any thoughts?