I had white coated tounge before. I went to an accupunturist - he gave me some herbs, and within a week or so my tounge became normal (pink again). I don't know what kind of herbs that restored it since he gave several kinds. According to the chinese medicine, your body is 'damp' when you have coated tounge. It could be candida if it's white coat and if it's yellow coat, it might be some kind of infection.
If you don't have a financial burden, it might be worth it to visit your local accupunturist who prescribes chinese herbs. And if you live in California, the insurance covers accupuncture.
hope it helps.