If you don't already have them: caves, hollows and sight barriers may help tone down some of the every moment fighting. This can be achieved by arranging rocks or driftwood in a semicircle or even capping it off to make a cave. This will give each fish a territory to claim and may instill "out if sight, out of mind."
A dense planting can also form a private area. Our local fish store sells a variety of aquatic plants at $3 a bunch.
I had this fighting problem among a group of cichlids even though I had a arranged the tank so there was a cave for each fish plus a couple extra caves. There was usually one less aggressive, most picked on fish that I would have to remove to a different tank. This would continue until I spotted that the problem was two very aggressive fish. These two were left to themselves. Eventually one outgrew the other. The smaller fish was left with mostly hanging out in it's cave (it had several cave openings to snatch food from, but still a bleak exsistance.) I set up a separate tank for it, where it lives happily to this day. I try different tank mates, so far unsuccessfully. Next I will try a large angel that outsizes either of them.
Something else you might try is quickly rearranging your tank ornamentation immediately before lights out. This will confuse the fish and cause them to establish new territories. This may diffuse aggression for a while.
Or like Jexnell said add more fish or change out your fish between tanks. These methods confuse the fish and can diffuse the aggression so one fish is not taking the brunt of the aggression all the time. Best of luck.