Both above posters are correct and give very good advice! The first step is choosing a tank. Some use a 10 gallon and say it works fine, but I'd recommend a 20 gallon to begin with. The reason is because it gives more room to hide out in if stressed, allows you to have more females which is better, and has enough space to keep the bioload down. Make sure your sorority has lots of hiding places terra cotta pots, rocks, driftwood, and caves all make excellent shelters for your bettas. I also recommend live plants as it is good for your fish's delicate fins, looks very nice, is natural, and helps maintain water quality. When choosing your fish, my recommendation is to choose siblings first. I breed bettas and I have sibling sororities and they tend to get along much better than females introduced in adulthood. If you can't get siblings, shoot for fish raised up together as this too increases your chances. If neither are available, look for females from the same source, whether this be a pet store, small breeder, or whatever else. Also check them for aggression, you don't want a female that flares insanely at the other females and looks as though she wants to kill. You also want to make sure though that the female isn't sickly and that's why she's calm, you likely already know what to look out for in a sick fish so I don't think I need to go over that. The ideal female will be calm, but active, and will be responsive to you but ignores or does not confront the other female(s). Make sure you have spare 2.5 gallon buckets, bins, or tanks available as many times sororities don't work out and fish need to be removed. Each separate bucket/tank will need its own filter and heater so be aware that instead of having one tank with several females, you can have several tanks with one female if it happens to not work out. Watch your females VERY closely for the first two weeks, after that point you can usually settle down. Tussles and fin nips are not abnormal and your females will flare and create a pecking order. It's important that through this time you leave the females to do their thing, but if a fish's fins become very frayed, they become way too stressed, or an actual fight breaks out, separate immediately. Sororities are an amazing experience and having successfully run many, I have come to love them quite a lot! They're definitely lots of work and heartbreak, but it's definitely worth it to see a group of such beautiful fish living in harmony. I wish you luck in the creating of your sorority, and please ask if you have any more questions!
