How Aggressive Is My Male Betta?

HI all, so I got this lovely male betta, and I'm toying with the idea of getting a 20 long and setting up a community tank.
I showed him the mirror four times, twice yesterday and two times today, for a period of less than two minutes. The first time, he swam to the other side of the tank with his gills flared. The second time, he flared his gills then swam away to the other side of the tank, but he stopped once or twice while swimming away and spread his fins out more. He didn't come back for a few minutes and hid behind some plants.
Today, he flared for less than three seconds and ran away, and I left the mirror instead of taking it away, and he wouldn't come within 6 inches of it but was watching it. The first time he flared a little while watching the mirror and the second he didn't.
Does this mean being in a community tank would stress him out too much? He made no move to attack and was skittish for a little while after....
Are there any other tests that wouldn't potentially kill anything (even pest snails) or that wouldn't stress him? Thanks in advance!

 

HI'm even reacting to the mirror at all would make me say don’t risk it but it’s your choice.

 

Okay thanks! Though, just to say, I was taking care of another betta that didn't react to the mirror at all, but he killed all his invert (it was just a 5 gallon) tank mates pretty quickly....
So even if the betta runs away, it does mean it's aggressive? Is it a behavioral thing, like is he checking the rest of his territory?

 

They are so different that way. I honesty have no idea if he would be good in a community tank but I avoid them so that I know there won’t be any fish deaths.

 

Thank you for your input, I'll leave him in his 5.5 gallon. One question, if you don't mind, do you think mystery snails are a good betta tank mate? I see it suggested a lot, but I just don't understand how that could be considering their long antennae.

 

Some Betta Fish will be perfectly fine in a community tank, others not so much. The only real way to know is to test it out. But just be sure to have that 5.5 g ready in case things don’t go as planned!

 

If you want to try your betta in a community tank without risking any injuries, I suggest getting a clear, floating breeder tank to put him in to see how he reacts to having tank mates. Expect him to flare a lot when he first gets in, that's just what bettas do. If he calms down quickly and for an extended period of time while having the other fish swim by him, you can try releasing him into the tank. Just be sure you have the time to watch them for a long time, like hours, with a net in hand in case anything goes sideways.

I used a breeder/isolation tank to introduce each of my female bettas into my sorority community and each took a different amount of time to calm down. Some only had to stay in the breeder tank for a couple minutes, some were in and out of there for a couple days. For the ones that took longer, I would let them out of isolation when I had the time to keep a close eye on them and when they got too stressed or were being a nuisance, I would put them back in to keep everyone safe. I would imagine with only one male betta this process would be easier!

The betta should definitely be the last fish you add to the community tank though, so he feels he's entering someone else's territory instead of the other way around. Just be sure to do your research before hand to pick good betta tank mates if that's the route you want to go. Like wrs2 said, keep his old tank up and running in case things don't work out. Even if they don't, you'll have a nice new community tank! Good luck!

 

Thank you both for your answers, I greatly appreciate them! And thank you so much for the write up, that's awesome!