Sorry aggressivefishrule, but my bettas in a 75 gallon do fine together (females)
With all the room to grow they are more active than the one in a 2.5.

As for a tankmate I have to agree with fishlover2009
Get a Malaysian Trumpet Snail, they eat leftover food and aerate your gravel, increasing the cleanliness.

I know with my 2.5 gallon it gets dirty FAST, so I orded some of those snails from white_roses90991, who is selling them. I will put one in my 2.5 and one in my 75.

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75 gallon:
8 Black skirt tetras
5 Red minor Tetras
5 neon tetras
2 Angelfish
1 8" Hi Fin Spotted Pleco
6 cory cats (emerald, spotted, albino)
3 amazon puffers

2.5 gallon:
Male Betta!

150 gallon saltwater:
In the works!