The initial plan was to have 3 clown loaches; and since there was a long time between when I actually got the aquarium and when it can be set up (I've had it for 4 months, it will be ready for fish in a week or so). When I knew for sure I'd have a sufficiently large home for them I bought them and put them in the 30 gallon tank - they're only 1.5 inches long - they have plenty of room.
The LFS doesn't do returns. I realize that getting him to another aquarist is probably my best option, but I really have no idea of how to locate one. I'm going to try a thread in Buy/Sell and Swap (Free giveaway to anyone with a suitable tank), if not I'm going to have to keep the fish; but I'm not enthusiastic about buying tankmates for it due to the size issues - and my LFS only sells tiny, unhealthy ones for a high price, when my friend bought his they had nicer fish.
So now I have a problem - I could keep the Bala shark alone in the 70g tank with the other fish untill I can find a home for it, which may be never, or I could get two tankmates for the bala shark and give them the 70 gallon tank - the clown loaches are easier to give away to a good owner, and will be ok for a year or two in the 30 gallon tank.