This goes to show that every fish of the same species is different. My red terror is at the bottom of the pecking order , my convict rules the tank , then my jd whitch is smaller , then the red terror. You may have got one thats extra aggresive , you can take him back and get another one thats not so dominent. What i do find interesting is its usually the new fish that gets beat up not the new one doing the butt whooping. Also was the red terror bigger than the other fish when introduced.
Is your festae under 6"? Just curious.