What tankmate can I get for my female?

[briser]

So I have decided that I think my little girl is pretty lonely and maybe that is what's wrong with her. She has lots of plants etc but she seems so bored. When I put her in a .75 gal she seems fine but when I put her in the 3gal she stops swimming around a lot after the 2nd or 3rd day.
When I bought her at the pet store she was in a tank with at least 30-50 other females and they were all getting along fine.. None of their fins looked bitten or anything.. Would it be okay to get her a female that she was living with before?

Any other suggestions?

[Malvolti]

Short answer: No.

Long Answer: Females only get along with other females if there are a bunch of them together which also means you need a minimum 10 gallon tank.

In fact most fish require a 10 gallon tank. The only things you might be able to add are a couple shrimp or an African Dwarf Frog. A 3 gallon is just too small for anything else.

It's unlikely that your Betta is getting lonely unless you neglect her (which I doubt). She could be bored, Betta need constant stimulation. She also might not like large spaces. If you put her back in the .75 gallon does she perk up? Does she stay perked up for more than a few days? It's possible she perks up because it's new and exciting. After a few days if she stays perked then you know she isn't lethargic from boredom but from size.

I have a boy that starts acting lethargic when I put him in his 5 gallon but when he's in my 1.5 gallon hospital tank he gets really active and makes nests. It's a security thing.

[briser]

When I put her in the .75 she is swimming around and playing in the plants and stays active the whole time, but it's not heated in the .75 cause a heater won't fit in it. :\