Garlic :)

[Reef_kid]

you have to remember that marine biologists are trained in a very different aspect of science. though immunology and microbiology may over lap
dosnt mean that those marine biologists know anything about chemical compounds or the nature of chemicals in a immunological or microbiological view
garlic has many chemical compounds that are used in medicine
and to treat infections. you have to also note that just because a fish is covered in white dots dose not mean it has ick. could be many other microbial organisms. just like when we have a sore throat or cold may be a bacterial infection such as S. pyognes or could be a yeast infestation

garlic has anti microbial agents as well as antioxidants and anti fungals
most of the time these are for protection of the plant itself but serves a purpouse in another aspect of the world just happens that it works in the fish tank on some micoorganisms

so yes garlic does have antimicrobial effects