Yes, I used Barkeeper's Friend (liquid version) on my DH's shower door which was covered with hard water marks and, mind you, wouldn't come clean with the stuff that is supposed to be used for hard water marks. The Barkeeper's Friend worked like a dream!

I've never used Barkeepers friend, but at least it's a household cleaner. Bath & shower gels are for our skin! Imagine what it's doing to our bodies.

Which type of shower gel is it? Many of their's are citrus based I believe, which is a great cleanser and the source of those fancy alpha-hydroxy acids in expensive skin care regimens.

Related - I recently found a silver chain that was badly tarnished. Of course all cleaning stuff that had been under sink in kitchen is boxed up, so I looked online for home silver polish recipes. Bingo - found one with boiling water, salt and baking soda. How easy is that? Except I can't find the baking soda in my temporary kitchen, LOL. Flash forward a week, watching cooking show and they demonstrate using ketchup to remove tarnish from copper pot. Hmmmmm...got out the ketchup, rubbed it all over the chain. Wiped off, worked good but not great. Tried the salt and boiling water with the ketchup, VOILA! Again, I think it is the acid in the ketchup...