How Sunlight Can Affect The Chlorine In Your Swimming Pool

Just like you, your pool requires some type of sun protection. Yes, you read correctly. Your outdoor fibreglass pool needs sunblock. But, before you run and squeeze a bottle of sunscreen into the pool, learn about how sunlight can damage the quality of your swimming pool water.


Chlorine: The Silent Anti-Microbial

Bacteria and algae love to thrive in warm and wet areas, like your pool. However, thanks to chlorine, these organisms cannot thrive in the swimming pool. What would happen without chlorine? Within a few days, the pool would turn into a cloudy, green, putrid mess- probably too unhealthy for you to swim. Imagine facing a green pool on a hot summer’s day?

That gorgeous sunlight you like to enjoy near the pool also affects the chlorine. The sun’s ultraviolet rays can cut down the chlorine concentration by 90% in as little as two hours. And on very hot days, the chlorine will deplete faster, becoming a cesspool for bacteria.

Chlorine: How Does It Work?

Chlorine is a chemical. You cannot simply dump bottles of it into the pool to make it completely free of germs. It needs close monitoring to ensure that your pool always has the right concentration of chlorine. If too much chlorine is poured in, you will experience eye and skin irritation. Put in too little or none at all, and you’re looking at a water park for bacteria and its close cousins.

With just the right amount, chlorine is an effective disinfectant. Once this chemical makes contact with algae and bacteria, it ruptures their cell membranes. This leads to the instant death of this unwanted organism.

Chlorine: Different Types

If you’ve never heard about the types of chlorine, then you might find this tidbit of information fascinating. First and foremost, not all chlorine is the same. Your swimming pool has a total concentration of two types of chlorine: combined and free. Combined chlorine is the substance that has done its part in keeping contaminants at bay. In other words, it is used chlorine. The free chlorine is the amount that will do its work. What matters most is how ultraviolet light affects this free chlorine.

To strike the right balance, both combined and free chlorine are taken into account. If the level of free chlorine dips below 1ppm, then your pool is not safe for swimming. This means the combined chlorine is higher, i.e. your pool is flooded with dead invaders. Would you feel like swimming in your fibreglass pool now?

Chlorine And Sunlight: What Happens When The Two Meet?

Potential bacteria and algae will deplete the free chlorine concentration in your pool. In addition, sizzling hot temperatures and sunlight will also react with chlorine. Your pool currently has free-flowing hypochlorite ions (free chlorine). Once it interacts with ultraviolet radiation, the ion breaks up at the molecular level. It transforms into a gas and gets freed into the atmosphere.

Also called chlorine degradation, you’d be surprised how this is. Just how quickly does the chlorine evaporate from your fibreglass pool? On a bright and beautiful day, with only two hours of sunlight, a pool’s chlorine level can deplete by up to 90%. This is probably why you see the pool serviceman running around every summer. These technicians add stabilizers and chlorine to make it a safe place to swim.


Chlorine And Heat: What's The Connection?

Ultraviolet light is not the only enemy of your pool. Heat is also a major player. When temperatures push past 28C, heat can also break down free chlorine. Bacteria love warm water. In fact, they proliferate the most in heated water. If there’s too many bacteria in the water, the concentration of free chlorine turning into combined chlorine becomes more. In other words, the free chlorine gets used up faster.

As a general rule, pool owners should put two times more chlorine into the water to uphold free chlorine levels for every 6 degrees Celcius the thermometer goes above 27.

There are so many things impacting the free chlorine, such as heat, ultraviolet light, algae, and bacteria. You are probably wondering if there’s a good way to balance chlorine levels. Rest assured, there is. This is where your pool technician steps in with a special cocktail of chemical compounds called stabilizers.

Chlorine Stabilisers

Cyanuric acid is a popular pool stabilizer or sunblock for your pool. It has a protective effect on chlorine. Sometimes pool technicians add compounds like trichlor and dichlor that release cyanuric acid. It helps with maintaining adequate chlorine levels. In other words, it lets you jump into your fibreglass poll on scorching hot days without a care in the world about algae and bacteria.

Cyanuric acid works by binding with the free chlorine in the water. This makes the chlorine stable when it is struck by ultraviolet radiation. Your chlorine will no longer break down. When sufficient amounts of stabilizer are added to your swimming pool, it enhances the effectiveness of the pool’s chlorine up to eight times!

How Much Cyanuric Acid Is Required?

To ensure your pool’s chlorine level stays maintained, a minimum of 30ppm of cyanuric acid is needed. It provides an effective shield from sunlight. Since there is significant variance in testing devices, ensure your pool’s cyanuric acid levels never dip below 30ppm. Ideally, you should maintain at 40ppm or more. The pool will be tested and rested until acceptable levels of cyanuric acid are reached. It is recommended that you conduct monthly testing to ensure sufficient cyanuric acid levels. This is necessary during the swimming season (for outdoor pools).

Too Much Cyanuric Acid: What To Do?

Once cyanuric acid is added to the pool, it lowers its pH. It makes the pool very acidic. To counterbalance this effect, sodium carbonate or sodium bicarbonate is added. This offsets the impact of a low pH.

What Is Cyanuric Creep?

Sometimes there is a certain amount of cyanuric acid already present in the chlorine. Examples are trichlor and dichlor (mentioned earlier). These are available in tablet form. When these tablets are put into the pool, they introduce small amounts of acid. It is important to keep the levels within range, especially according to the seasons. The use of trichlor and dichlor usually does require additional maintenance.

To enjoy your chlorine-filled fibreglass pool, it is important to ensure that it is regularly checked for free chlorine levels. Always keep your pool maintained with professional pool technician services. This will keep away harmful pathogens and let you enjoy your pool during the summer season.

How To Check Your Pool For Free Chlorine Levels

Checking for free chlorine levels is a straightforward process. Most often, a water testing kit is used, which includes a vial, reagent, and color chart. First, fill the vial with the water sample. Then, add the reagent (usually a DPD tablet) into the vial, which will react with free chlorine in the water and change its colour. Lastly, compare the colour of the water to the provided colour chart. The matching colour indicates the free chlorine level in the water. Please note, the light conditions can affect the results, so always try to perform the test in good lighting.

The team at Barrier Reef Pools Perth would be more than happy to help advise you on what to do if you need to test your pool water or if you are interested in the installation of a fibreglass pool.

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