Ask the Pool Guy offers theory about the green pools in Rio


As the explanations begin piling up from Rio about why the pools turned green and had to be closed, Ask the Pool Guy has been following
the developments and offers his theory as to what happened.

First, the chemical tanks ran out of “something” related to alkalinity and pH  this was likely an automatic dosing system for muriatic acid to control pH and Alkalinity levels in the pool water.

Next, seeing the green water at first glance or with panic workers thought to “shock” the pool to stop algae. With swimmers using the pool shocking with chlorine would have made the pool too high in chlorine for swimmers, so a non chlorine shock was used, hence the hydrogen peroxide addition.

The fluorescent clear green that we saw in photos is a likely clue to our team that the pH and alkalinity was very high. This can push metals out of solution and make them visible.

Adding hydrogen peroxide at pool grade levels of 35% (common pool grade levels) would have oxygenated the water, use up all available chlorine, and cause a drastic drop in pH/alkalinity.  Hydrogen peroxide, depending on what stabilizing agent is used in manufacturing has a pH of 1-6.5. Pool pH should be in the range of 7.2-7.6.

Finally the decision was made to drain the pools and refill with water from another pool. This is the best decision at this point as getting the water back to swimmable levels would take some time, and we are not sure how available the chemicals are in Rio at the quantities needed to treat these very large pools.

Water chemistry is an exact science. It is also a very complicated science and changing one part of the water chemistry creates a domino effect of changes in the water, and as you can see sometimes spirals out of control and can take quite some time to re-balance.

Let’s hope that the pool water being transferred into the pools has had better monitoring and filtration so it can remain stable and clear for the duration of the events!