Acara's are cichlids..... Cichlids are territorial and live with a strict hierarchy. It is in their nature to not be buddy buddy with any other cichlids and often when we place them in tanks with other cichlids, especially of their own breed..... we force them to do something that their biology does not agree with.... so if aggression erupts, like it will most of the time with cichlids, it should not be a suprise. Though, some like rams are more well suited to live with others of its species, there will always be the need to have its own territory and to set-up a tank heirarchy.
Bottom line, putting two cichlids in a tank which is naturally smaller than their natural habitat can make it so an occational dispute in the wild becomes a 24/7 ordeal for your fish. It is possible to keep cichlids together but just because a tank has been up and running for 3 or 4 yrs doesnt mean one day the fish will not decide they've had enough and you might have to remove one or more of the fish to avoid major health issues in your tank.
PS The behavior your talking about might also be courting behavior. The two; fighting and courting look very similar as the male tries to show the female his might. There is a fine line and the way to tell is to just observe the fish and you will def be able to tell after a time whether it was courting or fighting.
