Hi,
All chemicals are graded according to various grades, as follows:
A.C.S.: A chemical grade of highest purity and meets or exceeds purity standards set by American Chemical Society (ACS).
Reagent: High purity generally equal to A.C.S. grade and suitable for use in many laboratory and analytical applications.
USP Grade (United States Pharmocopeia), NF Grade (National Formulary), or FCC Grade (Food Chemical Codex): chemicals are manufactured in compliance with current Good Manufacturing Practices (cGMP) standards and that meet the requirements of the USP, NF, or FCC.: A chemical grade of sufficient purity to meet or exceed requirements of the U.S. Pharmacopeia (USP); acceptable for food, drug, or medicinal use; may be used for most laboratory purposes.
Lab: A chemical grade of relatively high quality with exact levels of impurities unknown; usually pure enough for educational applications. Not pure enough to be offered for food, drug, or medicinal use of any kind.
Purified: Also called pure or practical grade, and indicates good quality chemicals meeting no official standard; can be used in most cases for educational applications. Not pure enough to be offered for food, drug, or medicinal use of any kind.
Technical: Good quality chemical grade used for commercial and industrial purposes. Not pure enough to be offered for food, drug, or medicinal use of any kind.
You must use USP grade or above. You can usually find rather cheap USP+ grade CaCl2 on ebay or your local chemical supply store. You don't need very much to make a pint of 30% solution. It's definitely cheaper to make your own, but if you want 30% solution exactly, you need to dehydrate the CaCl2 first, then measure the weight and dissolve.
I'm not sure if the pool chemical you got is USP grade. Most likely, it is not. Then again, it might be, say, graded to technical or above, and actually be higher purity, but the manufacturer doesn't need to certify it as that purity, so doesn't pay for the more expensive tests and certification. I would feel comfortable buying USP CaCl2 from a reputable dealer and making my own solution, but not from a pool supply place.