Yeah you can actually put bettas in with other fish. I've had my betta in with other tropical fish before too. Where you will be putting the betta into an already inhabitant tank, it will feel like it is going into somebody else's home and knows he doesn't own it. So the betta won't think its his property. What I always did, for at least a day to two days, just keep an eye on the fish when you can, check and see if the betta is being chased or its chasing your tetras, check for bites out of tails, usually bettas will adjust fine. But if you see things happen within two days, then it's probably best to take the betta out. Hope I helped!