There was something that I heard years ago. When you add a bunch of chromis, eventually there will only be one.
However, I added 6 to my 240 about 6 years ago. Lost one in the first year.
But I still have the 5.
They seem to have a pecking order.
There is one, I would call the boss and I believe it's a male. He has a longer tail fin with small streamers. His dorsal fin is different from the rest.
Not sure if there are other males in the group, but there are a couple females.
They do spawn on occasion, but the eggs usually disappear in a day or so.
They are getting pretty pushy with the other fish. They will go at it with my Flame and Coral Beauty Angels, but it's only for a few seconds.