All types of chlorine are compatible with PoolRx. (IMPORTANT NOTE: If using Cal-Hypo granular chlorine (SHOCK), be sure to dissolve and dilute. BE SURE to dissolve each pound into a 5-gallon bucket of water before pouring in the pool slowly as you walk around deep end of pool, so it can further dilute. If you don’t, the PoolRx minerals make that particular type of chlorine so active and available, that if you just sprinkle it in, depending on your water chemistry, it can INSTANTLY OXIDIZE WHEN IT SETTLES TO BOTTOM AND TOUCHES THE SURFACE (you won’t have time to brush it up). The granular cal-hypo chlorine instantly turns black/grey. It will eventually go away after a few weeks, and there is an easy fix to clean it up sooner, but it’s totally avoidable if you just dissolve and dilute the cal-hypo before pouring in the pool. See FAQ #24: I made a mistake. How do I fix it?