I use "Mrs. Wage's Pickling Lime", and I think I got it in the grocery store once, and once bought it online.
The first C.H. I bought was called "Kalkwasser"
and is not highly recommended, even though it's what they use in delicate aquariums. (think of those fragile fish...) Still, I had a funny feeling about it. The Mrs. Wage's lasts forever.
( That Moreless drink really turned my health around. Lots of other folks too, with, like, degenerating knees, etc...)
PS, Lili, and others taking the borax solution, here's something neat to make with some of the borax. My mother used to have a large piece of amethyst we kept a bar of soap on, and this reminds me of it.