people are really misinformed about what you can and cannot put with bettas. Under normal cercumstances you can put any fish(that won't harm the betta) in with it, as long as it
a) isn't another male betta in a small area
b) doesn't closely resembe a male betta
Bettas have a reputation to rip apart any other fish but this is not the truth. They are only aggresive to other male bettas(and on occasion a female betta). The reason for this is becasue they live in areas that have small, encolsed places that they cannot escape (i.e. small ponds and rice fields) they defent their (small) area. They will attack another male betta untill one dies, but they will not just attack a fish passing by. They do this so that they can mate with females. They are fairly good tank mates for most community fish, but do not like to be in a fast boisterous tank, because they are so calm.