you transfer inverts and amphibians into large bucket/container(ie plastic bins can usually hold water just fine). Either give some mature media, plants, or change water regularly in said container. You then treat the tank and fish. Once fish are all clear and medicated water has been removed you transfer inverts and amphibians back.
Each to their own tho, use whatever method best suits you. I dislike the heat method and have always used copper to treat ich for years, its worked for me and thats all really.