I have a 5in dempsey and a 6in Managuense. All my other guys are smaller or less aggressive. The dempsey and managuense can't get along at all. They both have their territories on either side of my 240g, and if one crosses the imaginary line, all hell breaks loose. I was thinking that another similar sized aggressive male ( my 2 are males ) would break things up. Any suggestions for an agressive fish that will survive with a dempsey and jag? All help is appreciated. I have no females in tank.