I also have 3 NTT dats, 1 red devil and 1 flowerhorn and 1 african cichlidkillerfish;3351488; said:A 6'' flagtail ? i assume thats what you mean
Its worth a shot i've heard they can be aggressive twords each other so if the 6'' flagtail has been in the tank for a while it may chase the others around but since your adding multiple fish it should help to spred out any aggression so i'd say it could be done