Tilapia aggression problems

[Kate]

I have four Nile hybrids that just came into sexual maturity... One is a female. The dominant male started chasing everyone so I pulled the female out hoping to fix the problem. They were in a 55 gallon aquarium. I now have one male in a 20 gallon tub with live plants, one male in a 50 gallon drum and one male with the female in the 55 gallon aquarium. How do you keep these guys from fighting? I have tried hiding places too. I do have a pool set up with a breeder colony in it, but I was hoping to avoid mixing these two lines. Any suggestions?