I've added quite a few females and so far I haven't had any problems. The only violence I really had was between two of the first girls I added when they killed each other on the first day. This might be because I use a 56 gallon tank for my sorority, though. They have lots of room to hide and escape one another. I usually turn the lights off when I add a new female, though. Gives her time to get her bearings with a little less attention from the others. Good luck!