What is free chlorine

Bound and unbound (free) chlorine

If you start chlorinating the fresh water in your hot tub, the world will be fine. Any chlorine that you put in the water is available as free chlorine. The water is clear and almost does not smell of chlorine. When the chlorine reacts with pollutants, organisms, etc., a waste product is created. This waste product is the bound chlorine. The higher the proportion of bound chlorine in the water, the more the water begins to smell of chlorine and the eyes become irritated. Many users are now reducing the amount of chlorine added because there is obviously enough chlorine in the water. The water becomes cloudy and begins to smell.
A test with the test strips also confirms that there is sufficient chlorine in the water. The test strips always measure the total chlorine content (i.e. combined chlorine and free chlorine together). It is therefore possible that you measure a chlorine content of 2 ppm with the test strips. Actually enough chlorine. And yet the water is cloudy. What you cannot know: What is the proportion of combined chlorine and what is the proportion of free chlorine. Test strips cannot tell the difference.
The proportion of bound chlorine should not exceed 0.3 ppm. The proportion of free chlorine should be between 1.0 and 3.0 ppm.
 
How can I get rid of combined chlorine?
The bound chlorine is removed by shock treatment. During shock treatment, the combined chlorine is "burned". This process is called super-oxidation. You can use inorganic chlorine, Renew or SpaBalancer UltraShock for this.

How can I measure combined chlorine?
You cannot measure the combined chlorine at all. But you can with the Cool pool tester measure the total chlorine content (with DPD3 tablets). Then measure the free chlorine (with DPD1 tablets). If you subtract the value of the free chlorine from the total chlorine content, you get the value of the combined chlorine.

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