I was wondering if you have a sick fish and you put him in the hospital tank. when he gets well is there anything you should do about the water in the hospital tank. what if the infection is in the water???
Just do a 50% water change, change your filter cartridge and add new carbon. You'll be all set after that! Oh and add some aquarium salt if you have it.
most fish problems are normally present in a tank anyway
Its only a problem when a fish get rundown (much like us and colds etc) if they are weekened through stress etc the nasties can then take hold...