Summer’s soon to end, and we hope you had a wonderful time in your pools. However we know how hard it can be when the sun is shining and the weather is easy and the pool is green. How to explain to the kids that algae are responsible for hampering their fun?

The phenomena sometimes called “green pool” has to do with green algae proliferation, that’s correct. But it also has to do with the pool owner not properly covering their pools and taking care of the water pH.

This pool isn't exactly pristine. That's because it rained the night before slightly altering the water pH.
This pool isn’t exactly pristine. That’s because it rained the night before slightly altering the water pH. Image Source: homeyou

It’s true that it isn’t always easy to cover and uncover your pool during Summer, so what happens is that green algae can proliferate fast depending on how much rain and wind the pool water has to endure. This is because it’s actually the rain and the wind that bring to the water these marine creatures that rapidly multiply in warm, sunny weather.

The main factor for algae to flourish is indeed, the water condition. If the water pH is unbalanced, these algae spores that are brought in can bloom overnight. Controlling the water pH and cleaning the pool properly is a delicate issue.

Recently, in the 2016 Olympic Games in Rio, the swimming pools suddenly turned green due to hydrogen peroxide being inadvertently poured into the water, and once it mixed with chlorine, it caused seaweed to bloom. It was an embarrassing moment for the organization, showing the world how quickly our fun in the pool can turn into a problem.

Water turned green overnight at the Rio Olympic Games, causing concern and embarrassment.
Water turned green overnight at the Rio Olympic Games, causing concern and embarrassment. Image Source: BBC

So, in order to guarantee our children good times and our peace of mind, how should we proceed? There are two things to consider: one is prevention and the other is damage control.


As far as prevention you want to make sure:

  • Water is flowing adequately and the circulation system is working
  • You brush and vacuum the pool every day
  • The water pH is controlled

What is pH?

pH can be defined as the acidity of a substance. Since we’re talking about pools, the pH of the pool is actually the acidity of the pool water.

Why is it important to control how acid the water is?

It is important to control the water pH not only for the water quality but also for the pool and its equipment to work well and last longer.

If the water is too acid (pH is less than 7), chemical products used for pool cleaning/maintenance will not have the expected result. Most products are designed to be used in water with pH between 7.2 and 7.6.

If the pH is low, the swimmers will suffer irritation of eyes, skin, and mucous membranes.

The ideal pH is 7.2! It is a value close to the pH of the tear our eyes, exactly not to irritate them.

How to change the pH of the pool?

All pool stores have the necessary products for pH correction and measurement (for measuring test kits are used). If the pH is low (water is acid) you will use products that contain sodium carbonate. In the case it is high (water is too alkaline) products will take hydrochloric acid.

A standard pool pH measurement kit.
A standard pH measurement kit. Image Source: Piscina Fácil

The main problems that can happen if you leave the alkalinity of your pool at low levels are:

  • Water turns milky
  • Water easily takes on a green hue
  • Pool water is corrosive
  • Chlorine tends to lose their algaecide effect due to easy change of pH , and may take a greenish appearance.

What happens if the alkalinity of the pool is high?

  • Dull, non transparent water
  • Metal inlay in the pool pipes
  • Overspending with chemicals

Damage Control

Ok, so the pool is green and the children are mad. What to do now?

As far as for the kids, it’s damage control beyond our expertise. But as far as the pool, you can either take out all the water, which is not only unfriendly to the planet (water is precious), but also to your pocket. Besides, depending on the type of pool, taking out all the water can be harmful to its structure.

Physical Cleaning

In a green pool, we must first carry out the physical cleaning of all coarse dirt that is inside. Typically this dirt comprises algae, rotting leaves and other organic and inorganic materials that contribute to the development of even more algae. It is totally inappropriate apply to chlorine before realizing the physical treatment because, besides wasting products, toxic material would form in the water due to its reaction with organic matter. Such substances are called trihalomethanes and are proven carcinogens.

The correct procedure is to manually remove as many leaves and organic debris you can with the aid of the screen coupled to aluminum rod. This is a paramount task importance in order to avoid clogging of the vacuum pump, as well as to minimize the formation of trihalomethanes.


Now we must brush the entire surface of the pool, with brush connected to the metal rod , to loosen the algae that are adhered.

Correct alkalinity

,p>We should start by adjusting the alkalinity of the pool to just later correct the pH. That is because how alkaline is the water will make it more or less vulnerable to abrupt changes in the pH. After correcting the alkalinity with the appropriate product, wait 6 hours.


The next step is to decant all the sediments. In order to do that we use a clarifier. Turn on the filter and let the water circulate for 30 minutes. Then turn it off and let it decant overnight (12 hours).


If all went well, in the next morning your pool will already be much cleaner. It’s time for vacuuming! Since this is crisis management we are going to drain instead of simply aspirating. That is, we are throwing the sucked water into the sewer. For that we should just let the suction and the sewer open. The return register, skimmer and bottom drain must remain closed.


After the aspiration is done, most of the dirt may have been removed. So we can go ahead and add chloride to the pool. Since this is a shock treatment, you should be able to use a larger amount, that is usually specified on the label.

Clean the borders

We clean the entire border line at the height of the water surface with the aid of a dishwashing sponge, and a special detergent for pools.

Check the pH again

By now the pool is practically ready for use we just need to measure the alkalinity and correct it if necessary. Similarly, we must measure the pH and correct it if necessary. Finally , we leave the engine running with the suction records, skimmer , bottom and return drain open and closed sewage record. Okay, now the kids are good to go!

Pool has been cleaned and sanitized. The kids are good to go!
Pool has been cleaned and sanitized. The kids are good to go! Image Source: Mamma Prêt-à-Porter 

Another idea that can help you with this goal is the adoption of an automated physical treatment system. There are even robots that are able to assist you with many of the tasks! But that’s subject for a future post, stay alert! We hope you have a great end of summer and don’t forget to check our pool closing services.

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