Just want to add a couple of thoughts to the excellent points already put forward.
With aggressive fish in general, adding one adult to a tank containing one or more other adults who are already established is always a touchy proposition. The floating box idea might work, although I think that I would have placed the established fish into the box rather than the newcomer. But even then, you run the risk of the new guy taking over as boss and killing the original fish when you release it back into the tank.
I would suggest a complete re-arrangement of the tank interior...plants, wood, rockwork, everything. Rebuild every cave and shelter, alter every line of sight, make the new set-up as different as possible from the old. The idea is to place both fish on an equal footing in a "new" environment, so that neither has the established home-ground advantage. No guarantees, of course...the operation is still risky...but I think it is one of the best methods for reducing the odds of a blood bath.
Good luck, and please keep us posted on the results.
With aggressive fish in general, adding one adult to a tank containing one or more other adults who are already established is always a touchy proposition. The floating box idea might work, although I think that I would have placed the established fish into the box rather than the newcomer. But even then, you run the risk of the new guy taking over as boss and killing the original fish when you release it back into the tank.
I would suggest a complete re-arrangement of the tank interior...plants, wood, rockwork, everything. Rebuild every cave and shelter, alter every line of sight, make the new set-up as different as possible from the old. The idea is to place both fish on an equal footing in a "new" environment, so that neither has the established home-ground advantage. No guarantees, of course...the operation is still risky...but I think it is one of the best methods for reducing the odds of a blood bath.
Good luck, and please keep us posted on the results.