I agree that the ich was probably still in the tank when you added the fish in. Since fish can get ich easily from stress, then the damsels were very sucsebtable (sp?) to catching it from getting moved into your tank. If you have a hospital tank then the best method of treatment is hyposalinity. Hypo is lowering the salinity level to where ich cannot live. Its the safest and most effective treatment for your fish. You can do a search on hypo for more info.