I am using bromine cartridges and refilling with bromine pellets. The mineral cartridge is just is 98% Calcium carbonate

Looks up the chlorine msds and looks like it's just chlorine and maybe an oxidizer. I'd probably just out this stuff in it https://www.amazon.com/dp/B00AYJ0XK4/ref=cm_sw_r_cp_apa_fabc_VVHMJPMZMEBDZ8GDFS74?_encoding=UTF8&psc=1

This has done me pretty well as a one stop solution for my spa. https://www.amazon.com/gp/product/B00AYJ0XK4