try this...contact them first to make sure it's safe for your sink, but it's safe for fiberglass boats and showers and it is a MIRACLE worker on hard water stains. Non toxic, no fumes, etc. I post about it just about every other week because I am SO happy to have found it. You may be able to get a sample from the company or at Ace Hardware where I first found it. I will take hard water stains off glass and chrome as well as the plastic fixtures that look like metal. Porcelain sinks, tiles, etc. I have no connection to the company, just so darned happy with how this performs for me: There is another company with a similar name; be sure it's this one (the other may be good, I just never have used it). I've only used the creme in a jar, cannot say if the stuff in the bottles is the same or not. https://www.bio-cleanproducts.com/
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How to clean hard water stains
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