Not to start an argument, but I agree with Melosu. Garlic has been used in immune efficiency in humans, mammals, fish, etc for many years. Just a simple Google will also bring up a ton of Garlic studies showing the positive responses towards the immune system and there are fish studies conducted showing that garlic does not kill disease, but can extend the health before succumbing. As far as I know, garlic has never been proven to definitively kill parasites (primarily ich) in any ***reliable*** professional aquatics study. Of the freshwater studies, I don't believe any have been conducted without caveats.
As for food, I prefer a self-made mixture of frozen and fresh: sw
fish flesh, shrimp, clams, nori, cyclop-eeze, micro-small pellets, spirulina, etc. with a revolving mix every feed.