You are making two mistakes. One big, one little. The big mistake is using ultra pasteurized milk. Kefir grains do not like milk this dead. They would be happier in regular pasteurized hormone filled mega farm milk from the store. I'm serious. The little mistake is the occassional refrigeration. Kefir grains do not like it cold. This puts them into semi-dormancy. Keep them at room temperature. It will take two weeks with fresh changes of milk every day for them to snap out of it. At least you will notice some progress by then. So please be patient. They are doing the best they can with what they have to work with.