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What is a chemical free pool?

Doctors have been known to say that “The human body is a bag full of chemicals”. The following is one of the many definitions of a chemical that you can find on the web, all stating the same thing.

Ref: ThoughtCo.

“Matter and Chemicals

Anything that has mass and occupies space is matter.

Matter consists of particles. The particles may be molecules, atoms, or subatomic bits, such as protons, electrons, or leptons. So, basically anything you can taste, smell, or hold consists of matter and is therefore a chemical.

Examples of chemicals include the chemical elements, such as zinc, helium, and oxygen; compounds made from elements including water, carbon dioxide, and salt; and more complex materials like your computer, air, rain, a chicken, a car, etc”.

I couldn’t have said it better. I love it.

The meaning of a ‘Chemical Free Pool’

So now we must ask, “What do people mean by a chemical free pool?”.

Many of us remember the stinging eyes and that very strong chlorine odour we experienced as children and, that we carried home with us from our local pool. We can still experience it today, sometimes. That odour is given off by by-products of chemical reactions that are continually occurring in a pool and, generally, that is thanks to the addition of urea to the water via urine (mostly) and sweat. Good pool operators remove these nasty chemicals by super chlorinating (yes, by adding more chlorine) outside operating hours. The addition of that chlorine ‘burns’ them out.

It seems to be that because of these experiences, chlorine, like pesticides and coal, conjures up visions of doom in the eyes of many people and this has led to a desire for a “Chemical Free Pool”.

To bake a cake we grab, flour, sugar, eggs. butter, milk and produce something that looks, feels and tastes nothing like any of those chemical inputs. It’s the same when we add chemicals to a pool. The chlorine that can be quite nasty and difficult to handle, changes completely when added to the pool, just like the flour and eggs above.

Chlorine is a word that incorrectly describes many things. Chlorine is a gas, and quite a toxic one. Back in the ‘olden days’ chlorine gas was used to sanitise pools, so this is probably where the word, as used loosely today, originated. When we are told that someone is allergic to chlorine, we need to know what that chlorine compound is, that, that person is allergic to. I have yet to meet someone with that complaint who can answer that question.

Regardless of what we put in a swimming pool we need it to result in the chemical called hypochlorous acid. There are various ways of achieving this and it is this chemical that we need, in sufficient quantities, in a pool, to sanitise it. By the way, we have hypochlorous acid in our blood. It aids with healing wounds, apparently.

Why Hypochlorous Acid?

Fair question. There are lots of sanitising chemicals. However, we need something strong and efficient enough to kill bacteria and algae in a timely fashion that doesn’t cost a fortune. To qualify, a sanitising agent needs to be able to satisfy the ‘kill time’ requirement. This ‘kill time’ requirement has resulted from scientific research, where bacteria levels in a pool are tested at different sanitation levels. The sanitation level that results in a kill time that ensures the health of the pool patrons, is the level that is required in a swimming pool. The use of a chemical addition or process that results in the production of hypochlorous acid is the easiest way of ensuring that the sanitation levels required will be achieved quickly at reasonable cost. Check the active ingredient in the disinfectant you soak your baby bottles in.

What’s the Answer?

While we can never eliminate sanitising chemicals in a pool, we can run a pool on very low levels. This is done in Europe where there is an abundance of indoor pools. Chlorine by-products in indoor pools are of greater concern than they are in outdoor pools (as they, the by-products, are quite volatile). This is due to their accumulation in the air in the swimming pool area, if there is a lack of good ventilation. This accumulation is of most concern to pool operators and attendants who inhabit the environment for many hours a week.

The most common tests for chemical levels of sanitation in a swimming pool are described as follows:

“DPD No 1 tests for Free Chlorine or hypochlorous acid (HClO) to be more precise, a compound not an ion.  The important thing about DPD No1 powder, tablet, liquid or whatever is its buffering capacity (the ability of the DPD test chemical to lower the sample pH to the required level).  The pH of the sample must be between pH 6.2 and 6.5 otherwise you get interference from chlorinated compounds that maybe present in the sample.  At pH 6.35 all the free chlorine is present as HClO, none of it is dissociated into its constituent ions, H+ and ClO.

DPD No 3 is potassium iodide which when added to a sample containing DPD No 1 will react with chlorinated compounds such as chloramines.  DPD No1 plus No 3 provide an indication of all the chlorine present, free and combined.”

                   As advised by Noel Sampson CEO of Select Chemicals NZ. Noel is could well be the most knowledgeable analytical chemist in the swimming pool industry.

So, if the result of your test is 3 ppm, say, then you need keep in mind that the read is at a pH of around 6.3. The pH of a pool would rarely be that low. Generally, we aim at around a pH of 7.4 or 7.5. At a pH of 7.5 the concentration of Hypochlorous Acid will drop by 50% which would be 1.5 ppm for this example, and that’s ok. However, once the pH starts exceeding 7.8 the concentration of Hypochlorous Acid decreases until eventually it (the molecule) is no longer there. This means that a DPD #1 test is a useless means of testing sanitation levels without knowing the pH level of the water. pH must be tested at the same time and adjusted if necessary. It should be noted here that the combined chlorine is the combination of the various chlorine by-products that we need to remove from the pool. Total Chlorine – Free Chlorine = Combined Chlorine.

A more accurate sanitation read is the ORP level in a swimming. ORP means Oxidation Reduction Potential. The beauty of using an ORP read is that it reads the sanitation level of all sanitation chemicals in the swimming pool, not just the hypochlorous acid concentration as described above. An ORP sanitation level read itself doesn’t care about the pH level. If the pH is high and you add acid to the pool, that ORP read will increase rapidly as the hypochlorous acid molecule reforms. This happens without adding any further chemicals.

The problem with using an ORP read is that, like so many of us, we have been conditioned to the required 2 to 3 ppm DPD test level read of the chlorine level in a swimming pool. That’s a shame, because an accurate ORP read might tell us a pool is well sanitised while a DPD test of the same water might show a read as low as 0.5 ppm which will most likely result in panic stations by an operator. We have experienced this. It should be noted that an accurate ORP read requires a testing unit consisting of a quality, calibrated and proven probe that can accurately measure the millivolt activity in the pool, along with software that can accurately interpret that information, as well as a dispensing unit that will accurately and quickly adjust the chemicals as needed. Achieving this has taken years of research by scientists and engineers. These units are mostly used in waste water management.

Let’s face it, who really understands a DPD test, so why not have more faith in an ORP level? It should be noted, however that a pool operator is best guided by their local health regulations which may not acknowledge an acceptable ORP level but require a test giving a result in ppm (parts per million). A DPD test result is reliable and consistent, while an ORP read is dependent on the quality of the test and the test components.

What do we require to achieve minimal addition of ‘chemicals’ to a pool?

  1. Very good pool hydraulics.
  2. Debris control in the pool either by prevention or rapid removal.
  3. Bathers who have washed with soap and water before entering the pool.
  4. Regular toilet break habits by patrons, especially children and ‘partiers’.
  5. A pool free from patrons suffering from incontinence (even if temporary).
  6. The best possible filtration to remove the demand for chemicals.
  7. A flow rate that ensures a very high percentage of the pool water getting passed through the filter in a timely manner.
  8. Very reliable control of the chemical levels in the pool.
  9. Constant monitoring.
  10. Someone managing or monitoring the pool who will not cheat the system.

Is this possible?

YES. Swimming pool management has come a long way from the days when we went home reeking of chlorine. The combination of better pool hydraulics, filtration equipment, sanitation control systems and greatly improved pool management training have reduced the quantity of ‘chlorine’ and other chemicals added to swimming pools.

We see new products and new product (and sometimes deceptive) descriptions appearing on the market all the time. Every pool needs a reliable, proven and approved (APVMA) sanitation method along with reliable and efficient pool equipment which will allow for the good management of the levels of chemicals needed in order to get closer to that so called “chemical free pool”.

So, now, “What is a chlorine free pool?”

You will read about swimming pool sanitation systems that result in a “chlorine free” pool. Is this possible?

According to The Chlorine Institute “Chlorine is only slightly soluble in water (0.3% to 0.7%) depending on the water temperature”.

If you add hypochlorous acid to a pool using a salt water chlorinator (regardless of the chloride salt used) you are exposing the pool water to chlorine gas and I think it would be safe to say that there would be a very, very low quantity of chlorine (the gas) dissolved in that pool water.

If you add hypochlorous acid to your pool by using a granular chlorine for example I couldn’t tell you if chlorine molecules are formed in the water until the 0.3% to 0.5% concentration is achieved. It would probably be dependent on whether or not if chlorine gas, dissociated into its ions, is a reversible reaction.

The question should be “Is there such a thing as a chlorine pool?” That question was put to me by one of our service technicians and that question is what partly led me to write this article which hopefully clears things up a little. Regardless, there certainly is such a thing as a “Hypochlorous Acid Pool”.

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