What brand is it? It isn't HTH is it? If it's HTH, then that's Cal-Hypo and you shouldn't be using that in your spa unless you start with low CH and use this product instead of bleach and keep track of how much you add because for every 10 ppm Free Chlorine (FC) added by Cal-Hypo, it also increases Calcium Hardness (CH) by at least 7 ppm.