Hi, I have a fiberglass whirlpool in my home that is 20 years old and over the years, it has become stained. I've tried many products but none seem to work. Is the only solution to re-finish it or is there a product on the market that really works? I've seen ads for "do-it-yourself" fiberglass tub refinishing (costing roughly $80-$100), do you know if these products work and is it difficult to get excellent results? Or is it time to call in a professional?