Ha Killer Clowns sounds really scary! Fish are like people, every individual is different. The only real way is to try and if it doesn't work just sell them to someone else. There are a few techniques that could help your chances. I have seen people cut holes in a helmet crab cage and put it in the tank with the fish it the cage. This allows the fish get used to each other before you put them in. If your able to move your rocks that can help sometimes too.