How To Lower Combined Chlorine Levels? (The Best Fix!)

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How Do I Lower My Combined Chlorine Level?

Chlorine is essential for sanitizing and disinfecting your pool. But all Chlorine is not the same!  The Total Chlorine (TC) is the sum of Free Chlorine (FC) and Combined Chlorine (CC). Free Chlorine is the sanitizer & disinfectant. Combined Chlorine (CC) is just spent chlorine & not good for your pool. So, how to lower Combined Chlorine (CC) levels?

Shock your pool when the Free Chlorine (FC) is low and Combined Chlorine (CC) is high, to raise the FC level to at least 10 ppm. Run the pool filter for 8 hours (24 hours for a cloudy pool). Then add a Shock Oxidizer to break up the Combined Chlorine (CC) also known as Chloramines.

The additional Chlorine from the Shock and the Shock Oxidizer, progressively replace Hydrogen atoms by Chlorine atoms. The final product is Trichloramine which exits the pool as a gas.

Ammonia (NH3) ==> Monochloramine (NH2Cl) ==> Dichoramaine (NHCl2) ==> Trichloamine (NCl3)

The Combined Chlorine (CC) Levels will drop to near “zero”. The Total Chlorine (TC) level will be the same as  Free Chlorine (FC) level. It may be a bit high at around 5 ppm. 

Wait for it to come down to below 4 ppm (ideally 3 ppm) before diving in.

How To Lower Combined Chlorine Levels?

What Is Combined Chlorine?

Chlorine is used in two ways to sanitize a swimming pool. 

The first is regular chlorination, in which the chlorine source, such as Trichlor tablet, is placed in the skimmer, floater or feeder. The chlorine dissolves in the pool water at a slow, steady pace, creating Hypochlorous (HOCl) acid. 

The other way is to shock your pool. Shocking the pool is just super-chlorination or hyper-chlorination. 

The pool is shocked with a high dose of Liquid Chlorine or Cal Hypo, with a target of increasing the Free Chlorine (FC) by at least 10 ppm. Once again the result is the formation of Hypochlorous (HOCl) acid. 

Hypochlorous (HOCl) acid exists in the pool water along with the Hypochlorite (OCl)- ion as per the equation.

HOCL <=> H+  +  OCl-

Together HOCL and OCL- are referred to as Free Chlorine (FC). The ratio between HOCL and OCl- is determined by the pH of the pool water.

Free Chlorine (FC) sanitizes the pool by combining with the contaminants and forming chloramines. This is Combined Chlorine (CC). It no longer has the ability to sanitize or disinfect.

Total Chlorine (TC) is the sum of Free Chlorine (FC) and Combined Chlorine (CC).

TC = FC + CC

Pool Water Chemistry Testers give you readings for Total Chlorine (TC) and Free Chlorine (FC). So you can determine the Combined Chlorine (CC) as under:

CC = TC – FC

What Is a Good Combined Chlorine Level?

The short answer to this question is “zero”

I know that an absolute “zero” is not realistic. However, you should be concerned if the Combined Chlorine (CC) Levels are above 0.5 ppm. 

Target to keep Combined Chlorine (CC) Levels below 0.2 ppm.

Combined Chlorine (CC) is basically a Chloramine. You will know that the Combined Chlorine (CC) Levels are high in your pool when one or more of the following happen.

  1. Your eyes burn and skin is dry & itchy after a swim
  2. The pool has a strong ammonia odor
  3. The pool water is cloudy

Of course, every time you check chlorine levels, make sure to check both Total Chlorine (TC) level and Free Chlorine (FC) level, so that you can know the Combined Chlorine (CC) Levels too!

What Is the Maximum Allowable Level of Combined Chlorine?

The Pool Water Treatment Advisory Group (PWTAG) recommends that Combined Chlorine (CC) Levels should not be allowed to exceed 1 ppm.

The recommendations of PWTAG (TN61) for Combined Chlorine (CC) Levels are:

  1. Combined Chlorine (CC) Levels should ideally be “zero”
  2. Combined Chlorine (CC) Levels should not exceed 50% of Free Chlorine (FC) levels for FC in the range of 0 – 2 ppm
  3. Combined Chlorine (CC) Levels should never exceed 1 ppm, even for FC levels greater than 2 ppm

It may be noted that PWTAG does not recommend closure of a pool if Combined Chlorine (CC) Levels exceed 1 ppm, but recommends that the problem be resolved on top priority.

In any case, if Combined Chlorine (CC) Levels exceed 1 ppm, the pool may practically become unusable due to the pungent ammonia odor, skin & eye irritation and cloudiness.

For more information on Pool Chlorine Types refer to my post Complete Guide To Pool Chlorine Types. (What Is The Best?).

Recommended Swimming Pool Chemicals

Best Liquid CYA Free Pool Shock

Champion Liquid Chlorine (Sodium Hypochlorite) Pool Shock (12.5%) is easy-to-use, fast, and effective. This Pool Shock does not have Cyanuric Acid (CYA-stabilizer) and will not result in build-up of scale. Order from Amazon using the link below:

Liquid Chlorine Pool Shock (Case – 4 Gallons) – 12.5% Sodium Hypochlorite

Best Cal-Hypo Pool Shock

Calcium Hypochlorite Cal-Chlor chlorine granules, from In The Swim, provide 68% available chlorine for hard-hitting immediate results! Non-stabilized formula is ideal for super shocking or everyday use as it does not contain any Cyanuric Acid (CYA). Order from Amazon using the link below:

In The Swim Calcium Hypochlorite Chlorine Granular Pool Shock

Best Shock Oxidizer

SpaGuard Spa Shock Oxidizer eliminates soluble organic undesirable compounds and irritants in pool & spa water and is buffered to prevent pH bounce. Order from Amazon using the link below:

SpaGuard Spa Shock-Oxidizer

Thank you very much for reading the post. I do hope you found it informative and helpful.

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