pickling lime

I didn't understand some posts i saw in some other threads and i couldn't find them again so i opened this thread. What does adding the pickling liquid to your tank do(also whats in it)? What kind of pickling liquid do you use(brand, product info). How much to use? Were to get it?

Since i ordered some brain corals i thought it would be a good idea to get some cal/alk/mag tests just to make sure everything was where it should be.... well between my bank being dippy about releasing funds (they keep holding my payments as if my bank card got stolen, but they don't tell...