Your clown will be happier with another one. Their genetics go into full swing and they’re fun to watch. Your big clown is a female, if it was living in the last tank as the only clownfish. That makes them female. Or drop a male in with a less aggressive clownfish and it’ll boss the other around and turn female. Just get a tiny one. A tiny Ocellis will be unlikely to be seen as a threat. Your clown won’t kill it because it needs it. That being said keeping them segregated for several hours or a day cures a lot of aggression. Two clowns of different sizes can be ok, they know their place. 2 of the same size will have to “sort it out” to see who is going to be boss/female. My big black/white was donated to my local fish store, one of the biggest I had seen. I dropped several different clowns in with her without issue once they realize she is boss. Doesn’t take long. I settled for Sparky, a tiny (then) Nemo Ocellis. They live for each other all day long.

