I have had some really tough problems with hard water staining at my house.
Both the toilet and shower have bad orange stains from our high iron content in our well water.
Most cleaners "fumagate" me right out of the bathroom.
I did a web search on what is actually in hard-water stain removers. It's called oxalic acid.
Turns out, that oxalic acid is in rhubarb, which is why you can't eat the roots or leaves.
I happened to have some rhubarb plants in my garden, so I ripped off a leaf, tore it in pieces, and marinated it in a bottle of plain, cheap, white vinegar.
The next morning, I sprayed down the shower and inside of the toilet with the solution. I let it sit a while, then simply scrubbed and rinsed.
Rust stains came right off.
This is the best mineral stain remover ever!!!!!
Try it.
It you are interested. Read the "toxic effects" section of the "rhubarb" listing in Wikipedia.
Rhubarb - Wikipedia, the free encyclopedia