Ok, first you need to have an established tank with the proper lighting.
How long has your tank been set up?
What type of lighting do you have?
I have a condy, and it has been home to 2 different typs of damsels and 2 different typs of clownfish. It is now the residence of one Mr. Tomato Clown, and he hates to have visitors over!
I have had no prob with it trying to eat fish.
Also please don't get one just because it is cheap, make sure you can keep it alive first. Not trying to be hard, just watching out for our little aquatic friends...