This stuff is amazing. Powerful, use with gloves as it may irritate the skin. I put on my tough lime spots on my bathtub and sink, let it set for a few minutes and go back and wipe it away. Works well on plastic, metal, porcelain.

I live in Colorado and therefore have very hard water with lots of lime and calcium in it. Ugh, it gets on everything. This stuff will take that annoying white residue off, as well as rust stains and other nastiness. I could see the rust stains coming off as I was squirting this on my 50-year-old white bathtub. After five minutes of sitting, it was completely gone. I've also used this to get the mineral residue out of my clothes steamer and off my dog's drinking dish (it has a fountain and gets hard water stains easily).

I do recommend wearing gloves if you are going to come in contact with it because if it can dissolve hard calcium, your skin is hardly a contender.

It actually works! Nasty yellowish stains are gone.

This works so much better than any other product made for similar use. A rabbit rescue recommended it for cleaning litter boxes and boy does it work. Squirt some in and they look good as new again. I don't generally allow them to collect anything too nasty but had some in the past that were pretty rough and for rescues who may not be able to clean every litter box on a daily basis, this stuff is priceless.

A few months ago, I spotted a low price for this product on a deal website and -- since I'd recently noticed a stubborn ring of limescale in my toilet -- placed an order for it. It was scheduled to arrive a few weeks later, but Amazon said that it wouldn't arrive then and I could cancel or wait. Given the positive reviews that I saw, I decided to wait.

It finally arrived a few weeks later and I gave it a try this morning. I read the (slightly frightening) instructions, found something pointy to open the flip-top spout, and gave the bottle a few healthy squeezes to dispense some cleaner around the bowl. The instructions said to let it sit in the bowl for a while, so I closed the flip-top cap and took a shower. (I guess I expected it to be more "gel" or "cream" like, but it was pretty "liquidy". Not a problem, just surprised me a little bit.)

When done, I gave the bowl a few hearty scrubs with a toilet brush and the scale appeared to be gone. I figured if it did such a good job on the water-line scale, I should use the solution to scrub the entire bowl and under the rim, so I spent a few minutes really cleaning things up. I flushed and noticed that some of the blue dye remained on the bottom of the bowl, so I gave those areas some light scrubbing and when I finished, the toilet looks almost brand new.

I'm usually not a fan of cleaning with harsh chemicals, so I'm going to dig a little deeper into the ingredients to see if I can effect the same results with something gentler like citric acid crystals, but -- other than the possibility that I'm dumping somewhat harsh chemicals into the sewer system -- this product does exactly what it says it will do and if I can't mimic it more safely, I can see continuing to use it.