Betta + Corys is a good mix, gotta be careful with bettas + middle/top dwelling fish as they may get a bit territorial, depending on the betta obviously, one of my boys whos in with corys doesnt bother them ATALL when they are on the bottom but tend to notice at night if they are swimming around in the higher levels he will get a bit exited and chase them a bit, doing no harm obviously. But too look at a nice group of corys and a nice betta looks good overall