First be sure to recognize your cats’ language. Fighting and playing can look sometimes very similar. If your cats are just playing, they should be silent, with gentle biting, retracted claws, and chasing both ways. So if you see your cats biting seriously, fighting with claws, if you hear screams, or if chasing is only one way, that is conflict! The one cause of conflict is competition for resources.
FRIENDS OR FOES QUIZ
Cats don’t like to share. Give each cat their own food bowl, water bowl, litter box, etc. Put bowls in separate areas to avoid tension. Another potential cause of tension is introduction of a new cat. Cats need time to adjust to new friend. Cats do not "make-up" after conflict. Instead, tension remains permanent with signs more subtle like blocking, staring, etc. It will not get better with time.
Using FELIWAY MultiCat will help your cats live together in harmony. Use several diffusers if cats use different rooms.