Midwater fish?

[dmopar74]

Looking to fill out the tank with some mid water fish.

Current stock is black aro, clown knife, 5 silver dollars, pleco, and 4 polypterus.

Was thinking some severums, more silver dollars( lfs has 3 tiger sd's) or ?

 

[DMD123]

Some large balas? Mine are super active and my largest is probably 13"