I would have a hospital tank if i had room for it. Besides, I'm not sure about how I'd keep it cycled and everything while its not ossupied. So its a combination of laziness and lack of resources with me. But I figure, if a fish has something, then everyone else in the tank is exposed to it regardless, even before it manifests itself. So there is some sense in treating the whole tank. Its not very economic in that sense, i agree. But ehh...