First of all I have had clowns that used to lie sideways under a hob filter..healthy as horses and ate like pigs. I wouldn't necessarily push any panic buttons yet. Is there a nem or small area for it to hide? I would also be remiss to suggest a larger tank. 30g is best for this fish as is the golden rule for a lot of clownfish. I have raised them in a 15g to a fairly large size with a nem, but have since transferred them to a 140g. Much happier. If this is a very small fish you will be fine for a while, but you might want to try a small nem in the tank as well. But plan for a bigger tank.
