I didn’t think post #11 had anything to do with the schooling fish inquiry
These are the fish I assumed already exist in the tank to which you want to add a shoal ...
I still wouldn’t put pencilfish into this group
You’d likely never see any active hunting, just the slow disappearance of the pencilfish shoal
Congo tetras are a completely different sort &would be worth trying but add 15-20 not 5-10