As all of us have now been aware, the Rio 2016 Olympics swimming pools water turned green mysteriously, overnight.
More importantly, everyone was speculating to query what had have caused the problem because there have not been actual water testing variables are released to the public so far. Whatever the cause, this article is intended to provide some additional information for interested readers who want to know more about why the Olympic pools turned green and how you can avoid this in your pool.
Announcements from Olympic officials
The first official line was that after extensive tests, they had finally pinpointed the reason was chemical imbalance caused by too many people using the water. Mario Andrada, a Rio 2016 spokesman, said that there was a sudden decrease in the alkalinity in the diving pool, and that’s the main reason for the color changed.
FINA, the world swimming federation issued a press release and told the reason was the swimming pools were run out of some of the chemicals need to be used in the water treatment process. As a result the pH level of the water was outside the usual range, causing the discoloration.
New York Times reported, the director of venue management Gustavo Nascimento said that someone accidentally had added 160 litres of hydrogen peroxide to the pool prior 05 days to the incident and the electronic monitors had pick up the chlorine, but failed to notice that chlorine was no longer working.
Were the Olympic pools safe to swim in
The green color is not likely a problem itself, but an indication that there had been a potential failure of the maintenance process.
I cannot say for sure why this has happened due to not releasing of testing values officially by the relevant authorities. But, in a properly balanced pool everything other than Cryptosporidium will be dead in the water in less than 1 minute. But the Crypto requires 10ppm free chlorine maintained 24 hours in order for the chlorine to kill this.
Evaluating officials’ statements we can assume the reason could be the addition of hydrogen peroxide or the pH values were too far from the range.
What will happen if hydrogen peroxide were poured into a chlorine pool
Chlorine has both oxidizing and sanitizing powers but Hydrogen peroxide only has oxidizing power but unable to hold a sanitizing residual power. Hence Hydrogen peroxide would be suitable for a one time oxidizing shock but it will would not last in the water. In the presence of chlorine however the chlorine would act as a stronger oxidizer and actively oxidize the hydrogen peroxide. More specifically, Hydrogen peroxide (H2O2) reacts with Sodium hypochlorite (NaOCl) to form Oxygen (O2), Sodium Chloride salt (NaCl) and water (H2O). This would result in no hydrogen peroxide as well as no chlorine in the pool.
An equation showing that 0.48 mg of hydrogen peroxide removes 1mg of free chlorine.
The fact that it rained after this treatment would be a further likely condition that would surge algae growth since it is possible that the chlorine had been depleted by the hydrogen peroxide.
I had the same experience in Doha, Qatar
I experienced this in Doha, 2015. The particular pool was having a copper- silver ionization system and it had been maintaining 0.5ppm level of chlorine. One day the pool had been starting to turn green. Then the pool technician had added the hydrogen peroxide to shock the pool. The same time the water color h turned to black-green (See pictures).
This is totally unacceptable. Because Hydrogen peroxide must not use for copper -chlorinated pools but it may use for 100% chlorine free pools.
What will happen if pH values too far out of range
According to the statement of FINA, if the pH of the water was increased above the level of 8.5 then the chlorine in the water would simply not be able to do its job. Chlorine is most active (97%) at pH of 6.0 much more acidic no one want to swim in and at the pH of 8.5 the chlorine is almost completely inactive (12%) in the water so even if there was sufficient chlorine it would not be able to stop algae from potentially growing in the water.
Ideal pH range is 7.2 to 7.8 and the optimum pH for chlorinated pool water is 7.4 since this is the same as the pH in human eyes and mucous membranes and also keeps the chlorine efficiency around 53%.
What could be the reasons for Swimmers complain about stinging eyes and hair turning green
The swimmers complained of stinging eyes and strong chlorine smell in the water as well as green hair during the Games. The stinging eyes and strong chlorine smell could be caused because of sanitizer effectiveness and chloramines. Also worth noting is that pH out of ideal ranges could also cause eye irritation or contribute it. Green hair in a pool is a result of copper in the water. This indicates that there is in fact copper present in the water and that copper has been oxidized by hydrogen peroxide and precipitated out of the water.
Might other reasons for the green water
There might other reasons caused the green color in the pool water be poor filtration or Chlorine in the water but not able to work due to high Cyanuric acid or too high Phosphate or Nitrate ions
My Opinions to avoid this
My opinion is to consider the bather load increase during this type of event. It most likely let the chlorine drop to zero, or let the pH control system run out of acid which allowed the pH to climb unrestricted which resulting chlorine being unable to kill algae and other bacteria. Additionally to check and adjust the pool cyanuric acid level, if it is too high then it also could effect to chlorine efficiency where the chlorine is not able to do its job due to “chlorine lock”.
Furthermore, total chlorine, Total alkalinity, Copper and Phosphates correct values also more important to avoid this kind of incidents.