I did the same on an enamel cast iron pan and it was a perfect clean up. With as many sticks as I received, I want to try cleaning the mineral deposits out of my toilet bowl. I have tried to bleach the rings out of the bowl every few weeks and nothing has really helped. Some people swear by the pumice stone for removing toilet rings but I've tried on two different toilets in two different homes and neither looks as good as the photo below. Of course, neither is as FILTHY as that toilet bowl. Ew.
I read a lot of articles and reviews on using the pumice blocks to clean pools. I don't own a pool so I can't directly comment on how effective the Powerhouse Pumice stones might be but the photos I've seen show a lot of limescale and hard water stains removed off the tiles and the seams in between. I would give the pumice a try with a soft brush versus using chemicals if I had a pool.
https://www.amazon.com/Pumice-Cleaning-Stone-4-Pack-Density/dp/B016JQ9SG0/ref=as_li_ss_tl?ie=UTF8&qid=1501285058&sr=8-6&keywords=pumice+stone+for+cleaning&th=1&linkCode=sl1&tag=2010a7-20&linkId=68418da76adb73ec0fc16a62f6d13423 #powerhousepumice #elevateessentials