The leader died for an unknown reason, so everyone started fighting, and I decided it would be a good time to add a girl I have wanted to add but couldnt because I didn't want to see any nipped fins on these beautiful grils, but now that it was inevitable, I decided it would be okay, especaially because she now can't go anywhere else until I fund out what caused the leader girl to die, she was in a breeder box in the tank. I added her abut 24 hours after the first girl was lost, and it has now been another 24 hours and I still see some chasing and nipping. How long is too long?
Choclate is right. Try to cup them and float them in the tank for about a half an hour after redo the setup. It helps too to have it thick with plants with plenty of hiding places. If they nip it isn't really a big deal unless you see injuries other than a few peices of missing fin. If your alpha died they are just trying to work out who the next leader is. No one can really say how long it lasts. I have a fully established sorority and they still nip after almost two years. It's pretty normal. I would be more curious if you didn't have nipping. That would be weird to me.
There is no way to tell. All you can do is keep your eye on them. Nipping is normal and there really isn't anything you can do about it. If somebody gets extra agressive, cup them for a couple of days and float them in the tank and re-release. That helps a little.
It depends on the individual bettas. How bad is the fighting and nipping? That's fairly normal behavior but if its too aggressive - that's what you want to watch out for. Mine are so mellow, I cant tell who the alpha is. How much coverage do you have? The more crap you put in there, the less they see each other and won't fight as much. If they are still going at it tomorrow, I would take them out, rearrange the decor and release them one by one starting with the new one.
Well then there was no real fighting, just chasing and nipping, actually, there was some fighting at first, but then I added the new girl (she is bigger so I figured she could handle it, and she is such a sweetheart, she rarely picks on smaller fish) and it pretty much went down to nipping and chasing instantly, and she is liking the swimming room she has :D 30 gallons of it, compared to a cup before!