How does the sun affect the chlorine levels in your pool?

Updated: Feb 17

It is obvious that direct exposure to sunlight can impact your pool water. Just like humans, it will need to take preventive measure before exposing itself to the sun, and not just sunscreen!

It is not secrete that most pools need chlorine to avoid algae and bacterial growth. Without it, your pool with turn green and cloudy, and eventually you would not want to set a foot in there. When you add chlorine into the pool, it reacts with the lipids that make up organisms’ cell walls and membranes, destroying their cells, making it a crucial component to your pool.

There are two types of chlorine:

Free chlorine is the fraction of the total chlorine that’s available to disinfect the water, whereas combined chlorine is the fraction of the total chlorine that has reacted with organic matter such as algae and bacteria (it is the used chlorine). High levels of combined chlorine can suggest that there are too many intruders in your pool, and free chlorine is the chemical that needs to be regularly replenished.

What effect does sunlight have on your pool water?

Just like you would burn under the sun without sunscreen on, so does the chlorine in your pool. Free chlorine is the formation of hypochlorite ions, which are broken apart with ultraviolet radiation, which causes the free chlorine to be released into the atmosphere rather than staying in your pool. When your pool is under direct exposure to sunlight, the ultraviolet rays can reduce chlorine by up to 90% in only a few hours!

What is even worse is that during hot days, which is what we experience 365 days a year in Thailand, bacteria will breed faster even in water and without protecting your chlorine levels, the sunshine may have severe consequences on your water. Most bacteria grow better in warmer waters, so if you were planning on going away in the middle of summer and leaving your pool unattended, think again!

So, what can you do to avoid this from happening?

The key component here is to stabilize the pool, which can be done with stabilizers. You should be using enough to protect your water from sunlight, but not too much to the point where it slows down your sanitizer. You can also add UV Block into your pool, but rather than adding even more chemicals, you can bring your water to us and we will test it in our laboratory to ensure that your water is properly balanced.

If there is a significant lack of key chemicals, we will adjust and re-balance your pool to meet all necessary health requirements. Ensuring that your pool water is balanced will prolong the lifespan of your pool and ensuing a healthy and safe swimming experience.

Read more about our water testing services at:

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