Is the face bitten up ? Thats odd. There doesnt look to be too much damage. Im not sure but i think its really rare that polys kill each other because of aggression. Eating each other maybe way more common but there aggression usually is biting/ripping and holding onto fins. The reddish tail fin is normal for sens. Mine had it as qell
The first injuries were to pectoral fin, anal fin, and tail fin, causing them to turn red. The injured pectoral fin was shredded and the sen could barely use it. The only inhabitants are the 6" delhezi, 5" lap, 4" more, and 16" SAL. The injuries happened about 2-3 weeks after the introduction of the del and lap, whereas the sen has been in with the SAL for 8 months or so. The lap also took over it's spot on top of the sponge filter around the time the first injuries occurred. After the injuries had healed, I've saw the sen square off with the lap as the lap ate, like it was trying to pick a fight.