Join Date: Oct 2010
Location: New England, USA
Whoops, sorry... got dragged away from the computer...
Your tank size is fine. My sorority is also in a 20H.
Each betta is an individual... so there is no 'normal', really - just typical breed behavior. My Alpha is leader/teacher... she is kind and gentle, although she may give a young upstart a waring nip if they are need of one! She is the largest girl and the oldest in the tank.
Your Alpha may develop similar traits, or not. What concerns me is that her overly aggressive behavior may be suppressing the development of the other bettas in the tank... one of which may make a better leader for the sorority.
Watch your Alpha in the net breeder. Look for signs of illness - ill fish can be more aggressive. Also watch to see if any of the other fish are hanging around the net - if they have an interest in her. When the other bettas are comfortable with the Alpha and they are ready to accept her, they should consistently hang around the net to keep her company.
While the Alpha is confined, the other bettas will work out their hierarchy. Release the Alpha one a week, after a 30% water change and all the bettas have been well fed. If she behaves, let her stay out. If not, back to the net breeder she goes for another week.
Continue to do this until the Alpha chills out and gets along with others. If she's determined to be a monster, then she'll need to be removed to her own tank.
The dynamics in sororities are always changing, depending on growth, health, water conditions and so on. Sororities are challenging for this reason. The more you watch your girls, the more you'll understand what's going on in there! :)
There can be nasty fights... even the best sorority keepers have had horrible losses that just 'came out of the blue'. It helps if your tank water is as fresh as you can keep it, so the fish are less stressed. The bettas also need their tank to be heavily planted, with lots of caves and stuff to hide in.
Finally, the more bettas, the better... larger groups tend to be less territorial. Currently I have 12 girls in my 20H, with three cory cats... but, I also upped my filtration considerably and am committed to 30% water changes (min) every week.
Hope this helps. Let me know if you have more questions!
20H: 2 Cory Catfish, One very mellow Cambodian female Betta, Two Golden Veil Angelfish (male and female)