Tiger barbs are aggressive, so if you wanted them in a species tank, a 30 gallon should be fine. But if you wanted to combine them with other fish, they would probably need to be in a bigger tank for the sake of the other fish.
Bala sharks grow to about a foot as do clown loaches. Rainbow sharks get 6 to 8 inches long and need at least a 55 in my opinion. 6 or 8 tiger barbs would be fine. You could maybe do a firemouth with them.