I agree that short term use to get a picky fish to eat is ok. I honestly don't see long term use necessary or helpful.
I will be the sacrificial lamb & say that I have used it for my dog & currently for the horse. The dog was highly allergic to everything. I think it helped boost her immune system but I also used it mostly during spring/summer as I do with the horse to help keep bugs away. Garlic is in the same family as onions but not have the same toxicity level as an onion will affect a dog. My vet recommended fresh garlic, a clove or 2 per day based on the size of the dog. I can't remember if there is anything about the use of garlic on the website, but her name is Dr. Karen Becker if anyone wants to look.