well, the way it's treated in humans (bacterial infections) is that you treat it real strong for the first few days, and sometimes they either carry through with the same dosage until you're told to stop, or they slowly ween you off the drug. i'd say to give him full doses until shows signs of improvement, then slowly give him less and less until he is all better. or you could give him the full dose until he's completely better. either way works, you'd obviously have more of a success rate the latter way, but it's also adding more chemicals to your tank than you might need. every drug is different... i'd also suggest if you don't want to take my advice, to email the makers, or see if they can help you with their FAQ on their website.
fish really do have amazing immune systems... most of the time if you give them a little help, they can finish off the rest... but it's always good to either talk to the makers... so i advise that as the best course of action.
hope this helps, Marie.