When your pool starts to look a little cloudy or green, or if swimmers begin to complain about itchy skin or sore eyes, there’s a good chance your chlorine levels are too low.
In Western Australia’s warm, sun-filled climate, low chlorine level in your pool water is a common issue for most of us with a swimming pool. What many don’t realise is just how quickly sunlight can break down chlorine, even in a pool that’s been well cared for.
In this article, we’ll explain how UV rays impact chlorine levels, what signs to look for when things go off balance, and how you can protect your water using stabilisers and good maintenance practices.
Key Takeaways
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Low chlorine in pool water is often caused by sunlight exposure.
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UV rays can destroy up to 90% of chlorine in uncovered pools.
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Common signs include cloudy water, algae, and strong chemical smells.
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A stabiliser (cyanuric acid) helps protect chlorine from UV breakdown.
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Test chlorine, pH, and alkalinity weekly; stabiliser and hardness monthly.
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Use a pool cover, clean filters, and rinse before swimming to reduce chlorine demand.
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Professional servicing helps resolve persistent chlorine issues quickly.
The Importance of Chlorine in Pool Water
Chlorine is essential for keeping your pool water clean, safe, and hygienic. It acts as a disinfectant, targeting bacteria, viruses, and algae that can otherwise make the water unpleasant or even unsafe to swim in.
To stay effective, chlorine needs to remain within a specific range, ideally between 1.5 and 3.0 parts per million (ppm). If it drops too low, water quality begins to decline. Algae can grow, the water may become cloudy, and pool surfaces or equipment can start to show signs of stress. One of the most common causes of low chlorine in your pool water is prolonged sun exposure.
How Sunlight Reduces Chlorine
When chlorine is exposed to UV rays, its effectiveness deteriorates. Even on a mild sunny day, the breakdown can happen quickly. In an uncovered pool, as much as 90 per cent of the chlorine can be lost within hours. The stronger the sun and the longer the exposure, the greater the loss.
This is a particular challenge in Perth, where high UV levels are common. The more your pool is exposed to direct sunlight, the harder it becomes to maintain stable chlorine levels, especially without the right chemical support.
Signs Your Chlorine Levels Are Dropping
Sometimes the water makes it obvious. A greenish hue, dull appearance, or unpleasant odour are all clear signs of trouble. Other times, the warning signs are more subtle:
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Water that no longer sparkles or feels clean
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Small patches of algae in corners or around steps
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Red or irritated eyes after swimming
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A strong chemical smell, which can indicate chloramines
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Low chlorine readings, even shortly after adding sanitiser
When these symptoms appear consistently, it's important to test and adjust your water chemistry. If you’re noticing ongoing issues, especially during summer, it could be the result of low chlorine in pool systems that aren’t adequately protected from the sun.
The Role of a Pool Stabiliser
A stabiliser, often made from cyanuric acid, is used to protect chlorine from being broken down by UV light. It acts like a sunscreen for your pool’s sanitiser, helping it last longer and perform more effectively.
The recommended stabiliser range is 35 to 50 ppm for most outdoor pools. Falling below this level offers little UV protection, while going above it can reduce chlorine’s ability to sanitise properly. For indoor pools, a stabiliser is not required and should be avoided.
How to Use Stabiliser Correctly
Adding stabiliser is straightforward but must be done properly:
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Pre-dissolve stabiliser powder in a bucket of pool water
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Allow the system to circulate for at least eight hours
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Avoid cleaning or backwashing the filter for several days after application
Never add stabiliser granules directly to the pool, as they can damage surfaces or cause uneven chemical levels. If in doubt, it’s best to consult a professional for support.
Maintaining Water Balance Throughout the Season
As conditions change with the weather, your water chemistry can shift. During summer, when pools see more sun and heavier use, it’s essential to keep testing regularly.
Test weekly for:
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Free chlorine
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pH (aim for 7.2 to 7.6)
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Total alkalinity (80 to 120 ppm)
Test monthly (or with professional help) for:
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Stabiliser
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Calcium hardness
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Total dissolved solids
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Salt, if applicable
These tests help catch problems early, before they develop into more serious or costly issues.
Keeping Chlorine Levels Stable in Summer
Warmer weather puts additional demand on your sanitiser. Aside from UV exposure, factors like high bather load, sunscreen, dust, and garden debris can all contribute to chlorine depletion.
Some simple habits can make a big difference:
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Use a pool cover to reduce evaporation and sun exposure
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Clean your filter and skimmer baskets regularly
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Run your filtration system longer on hot or busy days
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Rinse off before swimming to reduce organic load
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Consider using a weekly shock treatment to restore sanitiser efficiency
If your pool uses a salt chlorinator, check that it’s functioning correctly and free of scale, as this can limit its ability to produce sufficient chlorine.
When It’s Time to Call in the Experts
Sometimes, despite your best efforts, chlorine levels won’t stay in range. This is often when deeper issues arise: from poor circulation to incorrect dosing or stabiliser imbalance. If your test results aren’t improving or your pool is regularly experiencing low chlorine in pool water, professional pool servicing can save time and prevent long-term damage.
At Pool Assist, we offer comprehensive water testing and chemical balancing, tailored to suit Perth’s specific conditions. Our technicians can check stabiliser levels, optimise your system, and recommend the right treatments to help you maintain consistent water quality, even during peak summer.
Don’t Let Sunlight Undermine Your Pool Care
Sunlight might be working against your chlorine, but with the right strategy, you can take control. Using a stabiliser, keeping up with regular testing, and making sure your system is running efficiently will keep your pool water clean, clear, and ready to enjoy.
If you’re still battling with fluctuating chlorine levels or just want peace of mind, let the experts take over. With more than 50 years of combined experience in WA pool care, Pool Assist knows how to keep your water balanced and your pool protected.
Book your professional service today and get back to enjoying your pool, without the stress of constant chemical adjustments.
Frequently asked questions
Q. Can I just add more chlorine if levels are always low?
A. You can, but it’s not always effective. If the chlorine keeps disappearing quickly, the issue is likely related to sunlight, poor stabiliser levels, or high demand. Simply adding more chlorine without addressing the cause can lead to waste and imbalanced water.
Q. Can I add too much stabiliser, and what happens if I do?
A. Yes, you can add too much stabiliser, which can lead to a condition sometimes referred to as 'chlorine lock'. When stabiliser levels go too high (typically above 70-100 ppm), the stabiliser over-protects the chlorine, making it less effective at killing pathogens and bacteria.
This is counter-productive and can lead to algae growth and cloudiness. The only way to significantly reduce high stabiliser is by diluting the pool water through partial draining and refilling with fresh water.
Q. What is 'free chlorine' and why is it important?
A. Free chlorine is the active form of chlorine that is currently available in your pool water to kill bacteria and sanitise. It's crucial because it is the actual disinfectant that works to keep your pool safe and healthy for swimming. You need to maintain a free chlorine level between 1.5 and 3.0 ppm in a standard pool.
Q. How often should I check my pool water chemistry?
A. For basic checks, pool owners should perform a simple test for chlorine and pH at least once per week. During Perth's hot summer months or periods of heavy use, testing twice a week is recommended. For the deeper checks (alkalinity, hardness, stabiliser), monthly testing by a professional is advised.
Q. Besides stabiliser, what else can I do to protect my chlorine from the sun?
A. You can significantly reduce chlorine loss from the sun and evaporation by using a pool cover. A well-fitted cover acts like an extra layer of sunscreen for your pool , shielding the water from direct UV exposure and keeping your chemicals locked in. Additionally, run your filtration system longer on very hot days to ensure good circulation of the sanitiser.