I have 3 females together since September. I havent seen aggression in the form of torn fins on any of them. Am not even sure who is the alpha altho I suspect it is Lucinda since I had her in May and only added Portia and IO in September. I had added another one, Electra, in September but she developed dropsy and passed away. Lucinda was the biggest but now Portia has caught up in size.
The live in a 20 litre tank (in Australia, we go by the metric system) and I think that is about 7 gallons.
Whenever I feed them, all three rush in front jockeying for position but they dont nip. I've noticed that they all swim together sometimes brushing each other when passing by but I havent seen anyone actually nipping the other. They do lunge at each other but once the "lungee" runs away, the "lunger" doesnt even run after her. Seems like a "watch my personal space" thing.
Maybe I am lucky that my 3 girls can co-exist.