Why is my pair of Angelfish fighting?

I have a bonded pair of angel fish that have breed and laid eggs before. The male is is a decent amount bigger and will sometimes chase the female around and nip her. Why is he displaying this behavior? Is there anything to counter act this? I used to have them in a 75 gallon and had to move them temporarily into a 40 gallon due to me moving. The male exhibited the behavior in both tanks.