Misunderstandings and Myths

Pool Industry Myth

A common pool industry myth is that when HOCl is used in a pool only OCl– remains. In reality, when HOCl is used, OCl– immediately converts back to HOCl to maintain the percentage division mandated by the pH. Although the actual reactions in water may be complex, a few illustrations in simplified language may help to describe what happens.

For example, if a pool contained 3 ppm total free available chlorine at a pH of 7.5, there would be about 1.5 ppm HOCl and 1.5 OCl–. If 1 ppm chlorine demand is introduced into the water, the myth would have us believe that as the demand is met, the HOCl is lowered to 0.5 ppm with the OCl– remaining at 1.5 ppm.


Assuming the pH to be unchanged, what actually happens is that the total chlorine is lowered to 2 ppm, the HOCl is lowered to 1 ppm, and the OCl– is lowered to 1 ppm. This happens even though it may have actually been only the faster and more potent HOCl that satisfied the chlorine demand. The subsequent shift of 0.5 OCl– to HOCl is virtually instantaneous.

The illustrations on the next page will demonstrate that:


Illustration 1 above:
Example one with one ppm chlorine demand, see explanation page before

If, under the same circumstances, 2 ppm chlorine demand were introduced to the pool, the 3 ppm total chlorine is still sufficient to satisfy the demand. Since part of the OCl– may be used in the process, the kill rate may be slightly slower, but the demand is met. The remaining 1 ppm of chlorine in the pool shifts almost immediately to 0.5 HOCl and 0.5 OCl–.

That illustrates the following picture


Illustration 2 above:
Example one with one ppm chlorine demand


Misunderstanding: Free Chlorine is not less effective at higher pH-Levels


Another myth or misunderstanding is that at higher pH levels chlorine is less effective. Actually, pH does not so much control chlorine’s effectiveness, but rather the percentage of chlorine in its most effective form (HOCl).
Thus, if the target HOCl level in a pool is 2 ppm, examples of how that target level can be met include maintaining 3 ppm total chlorine (pH 7.2, HOCl 2.0, OCl– 1.0), 4 ppm total chlorine (pH 7.5, HOCl 2.0, OCl– 2.0), or 6 ppm total chlorine (pH 7.8, HOCl 2.0, OCl– 4.0).

Following some important general information:

  • The more acidic the neutral anolyte is, the more Cl2 is found in the anolyte. As the pH-range of the ECA devices is between pH 6 and 8, less Cl2 is found in the Neutral Anolyte compared with Acidic Anolyte ranging between pH1,9 to pH3,5 . For this and many other reasons, the Neutral Anolyte is mostly the better alternative than the Acidic Anolyte.
  • The ORP levels change only, when the anolyte and the mixed water, that needs to be disinfected have different pH-values. The higher the difference between the pH-values, the more the difference in the ORP. The higher the pH-values of the water, where the Anolyte is solved, the lower the ORP.
  • Once the system is completely disinfected, the residual FAC is the most important value. If there is a residual FAC between 0,1 mg to 0,25 mg in the water, which needs to be continuously disinfected, the system should be protected from bacteria, virus and other types of harmful microorganisms. The trick of the game is, to find out, how much ORP and FAC the system is capable of accepting, the higher these values, the faster and more sure all harmful microorganisms and viruses will be killed.
  • As long the concentrations of the FAC is below 20mg/L (20ppm) in the water, there will be no unpleasant odor or taste in the water, as no reaction between aromatic compounds and the FAC will take place, and thus, no Chlorine Phenols will be developed.

Here you can find some ECA Water Applications


About Yasin Akgün

Yasin Akgün, of Turkish origin, was born in Munich on 22 May 1977. After completing his high school diploma he completed his studies of mechanical engineering at the TU Munich. Since 2006, he is the proud owner of the Munich watering place, which was in the inner courtyard of Fraunhoferstr. 13 from 1987 until 2018.
Since 2018 Aquacentrum has moved to Garching, a suburb of Munich.>More about Yasin Akgün in his biography
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