Hello Diana and welcome to fishlore!

Not sure if adding more fish will end up overstocking your tank.. but I noticed that you only had one rainbow in there. They really are a social fish that needs more of its own kind in the tank. If you added another or two, again not sure how overstocked it would end up making your tank, but you would see how happy they interact if you did. Maybe you can return the barb to make more room? Since the barbs do need to be in a group as well. But IMO the rainbows get along so peacefully with all the others that it would be my choice.

~ kate
EDIT: after adding up the adult size of your fish that you have now, you are indeed overstocked in that tank. I cannot really suggest more fish at this time, unless you brought back a few.