Free chlorine -- Tied up chlorine -- Total chlorine?  It's all chlorine isn't it? 

It's all chlorine, but only one type of chlorine is busy working to keep your swimming pool healthy.  Do you know which chlorine you're testing?

Here's a quick breakdown of what each chlorine reading tells any pool owner ...

Free Chlorine is the ACTIVE sanitizer in your pool.  It's busy killing germs, bacteria, and breaking down contaminants in your pool.  Free chlorine are your warriors.

Tied up Chlorine (or combined chlorine) is busy, but often times the chlorine becomes too busy to be considered active.  On the other hand, sometimes this chlorine is just spent and has worn itself out.  Either reason, the tied up chlorine in a pool is INACTIVE.  Tied up chlorine are tired warriors who either need to be free'd up or retired.  If these guys retire, they retire; if they just need free'd up, they'll usually go into the free chlorine zone and get active.

Total Chlorine is just the sum of the free and tied up chlorine.  When you add these two numbers together, sure ... you'll get a chlorine reading, but you won't know who your warriors are. 

Make sure you know which chlorine reading you're testing ... it matters in the life of a healthy swimming pool.