Amazing!
I have a humidifier that has a clear plastic basin that holds the water.  Lately it's been getting this weird cloudy hard film that won't scrub off.  I just poured this stuff into it and the filmy cloudy hard water buildup vanished.  I did take a toothbrush to a few of the hard to reach areas,  but with just a couple of passes,  the residue was gone.  You do have to be careful not to spill it on anything or let it sit too long because it can stain.  I did spill some in my tub and sink but I rinsed it right away and it was not a problem.  But later I found one little tiny dot that I must have missed and it's stained - very lightly though
Rating: 5 stars