There is really no evidence stating that garlic cures ich. It does however stimulate appetite. And there is a theroy that only the garlic extract (oils) helps. It is in that, the oils help repair the skin of the cloves if it is damaged, and I would assume they consider it being medicinal. You will see, perhaps in future posts of this thread, that people say they fed their fish garlic, and the next day there wasn't any ich spots. Pure coinsidence. Ich, and parasites in general go through stages of development that includes voluntarily leaving the fish. This is all they see.