Calcium Chloride ?`s

Ok, I know I have asked for help on many of things, so here we go again.  I am starting to use a 2 part solution for dosing and 1 of the parts requires calcium chloride.  I was recommended to use DowFlake, which I now have, but after getting it was told to be careful due to the change in the ingredients.  So here is my delima....what should I be looking for?    I am seeing many Snow & Ice Melts that state pure calcium chloride such as Sam's Club, Excel, and then seen threads on Prestone, but haven't found that in the store.  I have thought about buying some but afraid to.  So, any help or suggestions would be great.  Thank you.