Here is something that I copied and pasted from another thread that I made
i just decided to make a little sheet that had, commonly sold, easy to care for and cheap compatible fish for bettas
Some Betta fish will NOT tolerate tank mates and will go on a killing frenzy when introduced to other fish, so if you do decide to keep your Betta with other fish. Make sure that you have a backup plan incase It doesn't work. And make sure that you add the Betta, because this will prevent some aggresion. If you add it first then the Betta will claim its territory and then when you introduce the new fish the Betta will think that the new fish are in his territory and kill the fish
generally compatible fish for bettas
----Name of fish-------minimum tank size------minimum group number
Neon tetras-------------10 gallons------------ Six
Neons tetras can be a bit nippy when kept in small numbers so you would need atleast 6 to house them properly with a Betta
galaxy rasboras------------10 gallons-----------Six
pygmy cories--------------10 gallons-----------Six
most other cories-----------10 - 15 gallons -----Six
harlequin rasbora -----------10 gallons---------Six
non fancy female guppies------10 gallons ------- Three
endlers livebearers------------5 gallons---------Three
zebra danios-----------------3.5 foot tank-------Six
Bristle nose plecos------------2.5 foot tank-------One
Bushy nose plecos-------------2.5 foot tank------One
non colorful platies------------10 gallons---------Three
glo fish----------------------3.5 foot tank--------Six
rummy nose tetras------------10 gallons-----------Six
glo light tetras----------------10 gallons----------Six
cardinal tetras----------------10 gallons----------Six
X ray tetras-------------------10 gallons----------Six
"feeder guppies"---------------5 gallons-----------Three
Khuli loaches------------------2.5 foot tank--------Six
Scissor tail rasboras-------------10 gallons----------Six
Otos---------------------------10 gallons---------3 - 4
Bloodfin tetras-------------------10 gallons-------- Six
Rasbora Brigittae-----------------5 gallons----------Six
Black neon tetras------------------10 gallons-------Six
Yoyo loaches
Shrimp that are compatible with bettas
Ghost shrimp---------------------2.5 gallons --------one
Amano shrimp-------------------2.5 gallons----------one
Cherry shrimp-------------------2.5 gallons---------one
and a little note about shrimp, they are a hit and miss, some bettas are fine with shrimp and some aren't but all of my bettas have been fine with shrimp that are over 1 inch. I would suggest that a well planted tank with lots of cover should be used when having small ghost shrimp or cherry shrimp
sometimes compatible fish with bettas
---Name of fish---------------------Minimum tank size------minimum group number
male, and female Fancy guppies----------10 gallons-----------three
Honey gouramis -----------------------10 gallons-----------one
bright and colorful platies----------------10 gallons-----------three
Black widow tetras----------------------20 gallons------------Eight to not be as nippy
sword tails----------------------------15 gallons------------Three
Mollies-------------------------------15 gallons------------Three
Angle fish-----------------------------35 gallons-------------One
Gold gouramis-------------------------20 gallons-------------One
Lyre tail guppies-----------------------10 gallons-------------Three
Fish that are rarely compatible with bettas
IM not going to say all the stuff about groups and tank size, because I don;t even want anybody to try any rare compatibilities
Serpae tetras
other bettas
SA chiclids
Dwarf gouramis
Tiger barbs
Boesemani rainbows
Red tailed sharks
Any type of crayfish with claws over half an inch
i havent got the tank yet but i think i will be buying a 2.5 gallon tank or 5 gallon tank i still have to save up some more money to buy all the stuff i need and the fish tank
In a 2.5 your only option is really betta+ shrimp. 5 gives you more options, and as you can see 10 gives you alot more options I just recently bought a 5 gallon for a betta tank. I'm going betta, shrimp, and galaxy rasboras.