Are you sure that you're buying the right medicine for the sickness that you're trying to cure? There are two fish diseases: ick (which looks like white specks on the fish's tail) and fungus (which looks like greenish-yellow globes attached to the fish's tail). You have to use the right one or the fish won't be cured. Sometimes it takes more than one bottle, but I've never seen it take more than two. Let me know if that doesn't help you.