Yesterday I changed the water in my aquarium and then my dad bought some fish. He bought three gouramies. One of them looks healthy and is doing well, but the other two don’t eat. Both of them look weak, and I didn’t have such a thing with a gourami fish. One of them has a white spot on one eye and the other has a white spot on each eye. They don’t swim and they sit in the same place together. Help, what should I do??