Disease & Garlic

garlic is one of those snake oil myths that people use to get money from you at your LFS. even though it may treat ich, it should be only used once your fish get ich (i dont even think it does). otherwise, you will be creating strains that are resistant to the remedy.

i believe garlic is better at treating parasitic infections. the stinky part of garlic is sulfur, and internal/intestinal parasites just can't handle that. by ingesting garlic, you (or the fish) get rid of the parasites, who, ideally, flee in terror from the stench and burning sulfur chemicals coursing through your blood.
ich is best treated with heat (higher temperatures speed up the life cycle) and salt in the water (which kills the ich bugs when they reach the stage of the life cycle during which they are free-swimming in the water and vulnerable).

as far as being preventative or leading to overall better health, that's very much up for debate. either way, don't buy it from the LFS, just do it yourself at home. look at it this way- ich is most often caused by stress and bad water. if you're so concerned about the fish getting sick that you would go out and buy garlic food for them before they even get sick, you're probably also going to keep up on water changes and acclimate fish to the tank properly. overall better fishkeeping leads to overall better fish.

About 2.5 years ago I started feeding spirulina and garlic flake purchased from kensfish.com. All of my fish, including fry, are fed it one day a week. I have noticed that I have generally had fewer health problems as a result.