What is the difference between free chlorine, combined chlorine, and total chlorine?

  • Free Chlorine: all chlorine present in the water as Cl2(g), HOCl(aq) and OCl–(aq).
    • Free chlorine is the chlorine most commonly tested for with basic pool chemistry tests. Free chlorine is unused and available, just waiting to sanitize your swimming pool water.
  • Combined Chlorine: mixture of chlorine with organic amines or ammonia. 
    • Combined chlorine forms when free chlorine has combined with other chemicals in the water, and is therefore unable to sanitize or purify the water. This is the 'used' chlorine that has already done its job disinfecting the pool (chloramines – this causes the smell in a dirty pool).
  • Total Chlorine: the sum of free chlorine and combined chlorine.
    • In all instances, the level of total chlorine will always be above or equal to free chlorine levels.


Ideally, the chlorine reading of pool water will be between 1-3 PPM of free chlorine – that is, chlorine that is still able to clean your pool. Variables that affect chlorine levels beyond the scope of the Chlorine Genie are:

  1. Stabilizer levels
    1. Its purpose is to stabilize the chlorine in your pool water, so the sanitizer lasts longer. If Stabilizer levels are too low, chlorine can evaporate out of a pool.
  2. Water temperature
    1. The warmer a pool is, the faster chlorine will evaporate. Additionally, chlorine is broken down by UV rays, so if your pool does not have a cover, the chlorine levels will be lower. 
  3. Swimmer load. 
    1. The more swimmers a pool has, the more Free Chlorine will be converted into Combined Chlorine (due to bacteria, ammonia, etc.).

In order to increase chlorine levels in the pool, extend the run time of the Chlorine Genie.