Demasoni are rough on each other and can kill if you do not design their tank correctly. If you have caves or any place the smaller or weaker or female can be caught in and cannot get out a back exit, they can be killed. The secret to keeping demasoni without deaths is to have no dead end places. All caves must really be tunnels with rear exits.
I use PVC pipe. Lots of them. About 4 to 10 inches long. THe bully cannot trap the weaker in them because they simply go out the other end and into another pipe. I have not lost a demasoni in years due to bullying. Fry even grow in this set up with adults to adult size.
The same design can be make with rocks, slate, plastic stuff.
I know there are other hobbyists who successfully keep and breed demasoni. I wonder if they have other designs or use something similar to what I use.