My first try was ruined by two things. I'm using a 16 gallon reef nano tank with built in filtration. Some how a couple of the bettas managed to wiggle through the intake vent holes and made their way to the pump compartment. There one was sucked in, beat up, and spit out the return nossel. A second survived and was swimming in the compartment. Shortly after this a few of the remaining bettas showed signs of cotton mouth disease. I lost 4 bettas. 3 remained in the tank. 1 was small (I purchased as a baby) and protected in a breeder box. Eventually I had to separate the two adult females when they started to show endless aggression towards one another after about a week.
I was devastated and almost gave up on the idea of a sorority. The mix of colors and personalities in the tank though was worth trying for again. I bought 2 more girls and put them in other tanks to get them comfortable. Once I was satisfied they were settled in I put all 4 girls together.
Successful so far! One day was spent with my bright red female displaying her self as alpha. The pecking order developed quickly and as of today they are no longer fighting. Only one girl got nipped at (her name has been appropriately named Nip). I do know after they get comfortable in this tank they will probably try and go back to confirming each of their positions in sorority. Hopefully that'l be this weekend so I can keep watch. The first sorority gave me a good idea of how this seems to usually work. So far they're following the same behavior as the first set of girls.
I bought 3 more girls yesterday! I'll add these all at once probably around christmas time when I have plenty of time off work to keep watch. I may have to take Nip out of the tank so her fins can heal up - she may get nipped up even more (she's always the target of the alpha in this and the last sorority). In that case I'll add her back when I also add the baby (when it's grown).
This should eventually leave me with 8 girls.
I've been pretreating all my new girls with antibiotics and salt. Seems best after the experience I've had.
In the attached image you can see 3 of the girls on top (I have them trained to come up with tapping, since they don't always notice me right away). The alpha is on the bottom, she never took the tapping thing and doesn't always notice I'm there with all those distractions. You can also see false julii corydoras on the bottom (I have 8 of those now) and a CPO crayfish (which seems to work better with bettas than smaller shrimp). I intend to get more crayfish (this is the less aggressive type). He's too slow to hurt the girls and his pinchers are too small to do any damage to the corys who ignore him even though they're shy.
You can tell who the lowest ranked girl is. The one with all the nips! Her name is nip and she may have to be removed for being so overly docile and passive the alpha enjoys picking on her. The past day and a half though she's been left alone. The other girls don't have any real visible nips. When the alpha comes around they know to leave before the flaring starts. Nip is just too friendly to get the hint.