You need to seriously consider if you fish has one of the various forms of Ich or Brooklynella. Symptoms can include, not eating, spots on the body but not always, lesions but not always, slime around the head and gills mainly Brook, lethargic, fading color, erratic swimming, rapidly opening and closing the mouth, gaping at the surface of the water. Not eating is one of the symptoms. Below is a writeup I did for another posting. Sit by your aquarium and carefully determine if your clown has more of the symptoms.
Are you sure your fish have Ich or do they have Brooklynella? The treatment of choice for Ich is copper, I use ionic copper in a QT tank for four weeks. For Brook you have to use Formalin. The procedures for using formalin are as varied as the individuals you talk to. The most effective treatment is Formalin dips. Where you put 1 cc of 37% Formalin (Formaldehyde) in 1 gal of water and dip your fish for 45 minutes. You do this five times once every other day. I personally prefer Formalin in the QT tank. I put 1 cc to 10 gals of water every day for three weeks. Formaldehyde evaporates out of the water within two hours and is not accumulative. It does deplete the oxygen in the water so you need vigorous aeration with air stones. Do not use Formalin on fish that have open wounds, it will kill them. You treat the fish for BOTH conditions at the same time. Start with formalin dips then put them back into a copper tank. After 10 days of Formalin dips, once every other day they are cured of Brook then keep them in the copper tanks for three to four weeks and they are cured of Ich. The tank the fish came out of has to be fallow, fishless, for at least 6 weeks but 8 weeks is recommended by many writers. The eggs of Ich are in the bottom of your tanks and can lay dormant for up to six weeks. When they hatch they have to find a host or they will die. Brook's parasite divides and becomes a free swimmer looking for a host. The swimmer can persist up to four weeks before it dies. So a six to eight week fishless tank can say it is free of Ich and Brook. So you don't go through this in the future, QT all new arrives for at least 4 weeks.