In stocking a new fish tank I'm having some issues. The first fish to go in where a platy, guppy, and some long fin danios. 2 days ago I added a betta He got along with them fine. Last night we added some more platys, mollys, and guppies. Well the betta seems to have a real issue with these new guys. Flares up and swims around them. Doesn't attack them or chase. Then he will leave them alone and do his own thing, but if a fish get close to him he will flare up again. Today doesn't seem as bad as yesterday. It also doesn't matter if the fish is male or female and it is only the new fish. The fish that were in the tank before him don't set him off.

1 Is this normal? Is he trying to set the pecking order?

2 Should I change him out with my other betta that I know is very mellow?

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I just pretend I know what I'm doing

typical community betta with new intro's he is just flexing.

I think the new ones are taking some of his territory...lol

Alright thanks for the info. That is what I suspected He will just have to learn to live with less than a 40g territory. He still has his rock cave and moss ball bed. I don't think they will take that from him. Plus when they have babies the moss ball will be a snack machine for him

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I just pretend I know what I'm doing

they will attack but wont kill unless their lives are at risk.

They are survivalist aggressors. When I had mine in a community tank well when I had bettas he wasnt the biggest fish so that helped but when he was the biggest fish in his 15g he was a jerk.