When you are keeping bettas in a community tank we have to discuss good tank mates to keep with the betta. Tank mates that usually have success are Platies, Danios, Up-Side Down Catfish, Snails, Plecos, and Mollies. Other fish may work but these are the ones I reccomend. These all work well and usually have no problems.
Two major fish to avoid would be Tiger Barbs and Guppies. Tiger Barbs are knownfin nippers and since bettas have long flowing fins the Tiger Barbs will terrorize the bettas and shread their fins. This will stress the bettas out making them more liklyto get sick or even die. Tiger Barbs are a major no-no. Also Guppies and other long-finned fish would not be a good idea since bettas will sometimes attack them. I beleive is that the long fins confuse some bettas and make them think it is another male betta in their territory and attack them. Not all bettas will do this but some will so it is better to play it safe and avoid those fish just to be on the safe side. Other fish to avoid are highly territorial fish, large fish, and really aggresive fish.
Another thing to consider when you mmove a betta in to a tank with a filter is current. Bettas are not fish that enjoy fast moving waters. So do something to break up the water flow from the filter to slow the current. Or you can make a place or places in the tank with slow moving water current so the betta can rest. Also when choosing plants, if you choose plastic then becareful of sharp leaves that betta fins will get stuck on and rip.
But if you want to keep more than one betta in a tank you will have to keep females. Because as I'm sure you know the rule with male bettas is one male betta per tank. But with females it is one female per one gallon. So females are good for community tanks. But you have to be careful because sometimes females are just aggressive as males. So when you are picking the females for the tank pick the shyer ones from a community tank. Do not buy females that were jarred by themselves if you plan to keep them with other females. These females tend to be more aggressive and territorial. Also when you add the females add all of them at the same time. At first there will be some fighting and showing offs. This will stop once a pecking order is set up but occasional bites will be given out. If one female is particular is either really picked on or really aggresive then remove it. Everytime you add or remove females then a pecking order has to be re-established. Bettas are easy to keep in a community.
