i would move the bala out of there and into a tank with other balas. they do like company of their own kind. if you would like to have a community shark-like fish in there i would suggest a rainbow shark or a red-tailed black.
definitely add cories! as for top/middle swimming fish, you could go with long finned rosy barbs, they are beautiful. i have a few of them and they are good with smaller fish, although they may eat tiny fry (but that would be ok, since it keeps tank populations down!).
definitely add cories! as for top/middle swimming fish, you could go with long finned rosy barbs, they are beautiful. i have a few of them and they are good with smaller fish, although they may eat tiny fry (but that would be ok, since it keeps tank populations down!).