So I bought my fiancee a male Betta for mothers day, and it's crammed in a little Betta tank. I felt bad for it and picked up a 20H yesterday. Now I know you can't put other male Betta's in together but what about other tankmates? I was wanting to put a small school of Cardinal Tetra's and a Cory cat or two in with him. Will there be any issues, or are they pretty much a one fish one tank deal?