I swear by neon gobies. They're captive bred and easy to feed if theres nothing to pick at.
I was under the impression that ick (Cryptocaryon irritans) was an external parasite. It adheres to the skin of the fish, makes its way into the mucous layer and into the epithelium. While at this point anything attempting to "eat" the parasite off of the fish would be ineffective, the initial "spots" found on the fish as tiny salt grains would be halted from completing the life cycle.