Yesterday I bought 3 balloon mollies to put in a 20L tank, which I also added my male Betta shortly after. How long should it take for them to get along? My Betta was a little defensive, not attacking the mollies, but showing signs of flaring. The mollies are hiding at the moment.

2 Answers 2


Betta can be housed with various other fish but in your case, you're short on space. 20L (5 gal) is about what is recommended for only a betta. Various sources seem to place the min tank requirement at 75L (20 gal) for mollies but some say 37L (10 gal) is fine. So as you can see, the your best guess would be to upgrade to a large tank or to split them in two tank. The betta in your current one and a larger for the mollies.

If you do split or upgrade please make sure the tank is/are cycled before getting the fish in them or you risk loosing some/all.

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    I agree that the different recommendations for the size exist. Since Mollies are eating machines, the lower size aquarium will need a very well monitored and maybe sophisticaed filtration. Large tanks are usually easier to manage. Commented Jan 9, 2017 at 18:02

You don't put any other fish with Bettas. The Bettas will stalk the other fish and from time to time bite off a big chunk of their fins. They have big mouths and sharp teeth, and are extremely aggressive.

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    This is definitively not true, betta can be housed with other fish, they simply need to have their personal space. I currently have a betta with a small school of neon tetra in a largish tank (75gal) and they get along pretty well. -1
    – Rémi
    Commented Aug 12, 2016 at 19:24

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