Most cheaply sourced de-icers are not going to be anywhere near 100% calcium chloride. It's one thing I'll give Pool Stores credit on, the CH Increaser that they sell is high purity calcium chloride. All calcium chloride manufactured in the world comes as a by-product of the Solvay process whose end products are soda ash (sodium carbonate) and calcium chloride. Good quality "snow melt" chemicals are mostly calcium chloride because the hydration reaction is very exothermic and produces enough heat to overcome sub-zero freezing temperatures as the freezing point depression of chloride salts is limited below a certain temperature. So if you live in a cold climate, you can always tell a cheap de-icer from a good one because only the good ones will work at low temperature.
If the ice-melt product is coming from China, well you can almost bet that it is not going to be high purity. There will likely be a significant amount of salt in it and possible magnesium chloride and sand. If you do buy it, I do a bucket test on the material you get to see how it affects pH, TA, CH and salt levels. You can do a bucket test. If my math is correct (doing this on the fly) - 1/4 tsp of pure calcium chloride in 4 gallons of pool water should increase your CH by 200ppm (roughly). You can take your product, add a 1/4 tsp and see where the CH goes. The amount of CH rise you get will give you an indication of how pure the material is.
