hi,
I had the same problem getting them to live. I found that the bigger they are when you buy them the better chance they have to survive. Small clowns are usually not long out of quorintine and they have been treated for diseases and upset alot so tend to die easily under new tank conditions. If I was you I would buy four or more off someone who has had them for a while. Also when you add them to the tank leave them in the bag in the tank for an hour or so and every 10 or so mins add 100ml of tank water. scoop them from the bag and place in tank. Never add the water as that introduces disease to your tank. A lot of babble hehe but hope that helps.
Malc.