clownfish sick

[cowboy]

i have a clownfish that has a white spot on his body were his front fin meets his body one under his mouth the corner of his mouth is white. he is eating but sits on the substrate. i've had him for 2 yrs. i've added no new fish to the tank in almost 6 months. i don't have a hospitle tank because i didn't plan on adding any more fish. i have a 20gal tank with a sea horse in it. can i use that tank and add meds with out hurting the sea horse. my water para. are great. i do regular water changes. this is the first problem i've ever had with a salt water fish. i have othe fish in the tank and they look fine for now. can any one help.
thanks cowboy

[billsreef]

Does the white spot look like something attached to the fish, look like a pimple, or simply look like a white area of skin?

Any other symptoms such as rapid breathing or scratching?

Done any water tests lately? What are the parameters? Actuall values help more than simply saying they are great.

What size tank?

What are the other tankmates?

I realize this sounds like a game of 20 questions, but it the best way to paint a mental picture of the situation to enable us to try and help you and your fish. If you have access to a digital camera, a picture is worth 1000 words of course ;)