I've been operating municiple public pools for about 18 years and one of the first things I leaned is to never buy chemicals from pool stores. I go to the local chemical wholesalers and purchase Bicarb/Calcium chloride in big bags. There is usually a minimum purchase amount ($250 where I went a couple years ago - still have lots left!). The only issue I had at first was caking due to storing in an unheated building but a cheapo plastic storage bin (with sealing top, not the kind with two halves that fold down) solved that problem. I keep unopened bags in the basement heated storage and the opened ones in storage bins.

Caking of the bicarb wasn't a big deal as it breaks up easily enough. Caking of the calcium chloride is a royal pain in the bum.