My common goldfish has big white spots on the side of his body. What is this?

The rest of his tank is covered with a white "pulpy" or "moldy" substance. I am treating him currently for fungal infection. Is this right? He is also extremely lethargic, except for when I feed him and then he only eats like maybe one or two flakes. I also just recently moved him into a new aquarium so I want to make sure this does not have anything to do with it. Thanks for your help.