JennM;369485 wrote: How long have you had the fish? Any new additions lately? Any sudden changes to parameters?
Speaking of parameters... what are they?
Are you certain it's ich? Clowns don't get ich very often - it is possible, but there are other ailments it could be too - and it's best to be sure of what you're treating before you quarantine and begin treatment.
Running on the careful assumption that it's ich, you can spike the food with some garlic, that will help entice the fish to eat, and help boost its immune system. Meanwhile, try to figure out what caused the outbreak in the first place (see my first questions) and if there is an issue there, correct that. If the underlying cause is not addressed, you won't solve the problem by just treating the symptoms.
If you have a QT, you can use hyposalinity and/or Cupramine by Seachem - and get a copper test kit with it to monitor the dose.
If you can't do that, get Seachem Metronidazole & Focus, spike the food with that in a 1:1 ratio - one part Met with one part Focus (you can make a batch by thawing some food adding the med and refreezing). It's hard to overdose Met. That medicated food can be used safely in a reef tank.
Hope this helps,
Jenn