This is my understanding of it. I still haven't quite gotten the hang of this but I'm sure an expert will post sooner or later and explain in more detailor let me know what I got wrong. Here's a quick formula for the chlorine: TC-FC=CC. FC is the good chlorine that you want to have in the pool. It's what combats all the "gunk" in your pool. CC is "bad" chlorine. If this number is high, it means your chlorine isn't doing you much good. Ideally, you want this number (CC) to be 0 and you want the TC and FC numbers to be the same. You can do a search on this site and read ALL about what these numbers mean in relation to one another and why they're important to know. Again, someone PLEASE let me know if I got any of this incorrect. This is what I've gleamed from reading this site and the sister site. I noticed noone else had posted yet and thought a LITTLE information was better than nothing for ya.