Fish 4 all, you did it again, youre in the salty sections. Clownfish, not Clown Loach. :D
First, I need to know a bit more about your tank. The appropriate methods for curing a problem vary greatly depending on your livestock and other considerations.
Please Read this: http://www.fishforum.com/viewtopic.php?t=1802
in the meantime, try to obtain a photo of your fish and/or google "Marine Ich" and see if that looks like your problem.
If you have any corals or other inverts (snails, crabs, ect) in the tank, you may need to invest in a 10 gallon quarantine tank.
If your fish does in fact have marine ich, you may also want to add a UV Sterilizer for a few weeks. this will kill off the ich
Regardless of the problem, you MUST seek out the cause of the problem and correct that. If you have marine Ich, it is because your fish is stressed that it suffers from this problem. Ich is ever present in most aquariums, fresh and salt alike. A stressed fish enables the parasite to host. This is true with most fungal infections as well, a healthy fish has a slime coating that protects the fish from such problems.