I just established my first ever betta sorority. 4 females who were all introduced to the tank together (first given only visual access to each other, then allowed to explore freely). After a few days of chases and a bit of fin nipping they had settled down quite nicely (especially after adding some rasboras, which seemed to distract the bettas from each other).
But I'm currently fighting an attack of columnaris, and have already lost two of my females. The two remaining females aren't bothering much with each other, but everything says you should not keep only 2 females together. What I'm wondering is what is the procedure for adding new females to a tank with existing females who already have staked their claim on the tank?
(Of course, this is assuming that the treatment is successful and I wouldn't dream of adding more fish until the tank is healthy again.)