I'm quoting SuperD:
"Ich can only be cured in the free swimming life stage of the protozoan. There are two main approaches to curing Ich, and opinions vary on which is the more effective. Malachite green and formalin is sometimes used to cure the disease (note that malachite green is hard on scaleless fish like catfish and loaches, and also other fish such as tetras). Some alternative medications are based on copper and formalin. The other method is to add salt to the tank (gradually), up to a level of 1-2 tsp per gallon. Note that fish vary in their tolerance of salt, and for more sensitive soft-water species, it may be better to use 1 tsp per gallon maximum. If you are treating in a planted aquarium keep in mind that higher salt levels may affect plant growth. In either case, increasing the temperature to no more than 86°F should kill the parasite off more quickly. However, increasing the temperature means there will be less oxygen dissolved in the water (some medications can lower it too). Due to the life cycle of the parasite, the whole tank must be treated, in order to kill the parasites which are not attached to fish. Therefore it is not appropriate to treat only the affected fish in a separate isolation tank. Note that when a fish has been cured from Ich they will usually form an immunity to the infection."
I would start with the salt treatment, gradually adding the salt & raising the temperature slowly.
