Buzzy, your tank is not cycled. Get some Ammonia, nitrIte and nitrAte test kits asap. Clowns are very bad fish to cycle a tank with. Ammonia and nitrite spikes will likely make them sick or possibly die.
Test your water. If there is ANY ammonia do a water change. Add an airstone or lower the water level so the water splashes into the tank.
Read about the nitrogen cycle.
http://faq.thekrib.com/begin-cycling.html
Or take the clowns back and get some tougher fish until your tank is cycled. Do you have a friend with a mature fish tank? (older than 6 months?) If so, and if you're sure it is a healthy tank, maybe you could ask them to give you some gravel, or a piece of their filter media to add to yours.
Barring that, try to get some 'ammo loc' or some Prime water conditioner. It will help to detoxify the ammonia and nitrites.