It’s frustrating when your salt chlorinator appears to be working – the lights are on, and the monitor shows everything is fine – but you still can’t get a chlorine reading in your pool. This is a common issue many pool owners face. Let’s walk through what might be going on and how you can fix it.

Key Questions to Consider:

• How does your pool look? Is there any visible algae?
• Do you notice brown dust that clouds the water when you brush the pool?
• What is the salt level in your pool water?
• Are you using an Eco pump, or is it a standard single-speed pump?
• Have you added stabiliser to the water recently?
• Do you use a pool cover regularly?

Why Can’t I Get a Chlorine Reading?

If you test your pool water and can’t get a chlorine reading at all it may be due to very high chlorine demand. High chlorine demand is the inability to keep an adequate level of chlorine in the pool water even though the water appears to be balanced and properly maintained. The pool water is consuming chlorine faster than it can be produced by your salt chlorinator or added through chemical applications. The result is zero detectable chlorine, even though you’re adding it regularly.

What can cause high chlorine demand?

1. Algae, bacteria, or fungus growth.
2. Debris or contaminants from winter or periods of inactivity.
3. Heavy pool usage or high bather load, especially during summer.
4. Biofilm or organic material in the water, such as sunscreen, leaves, or algae.
5. Pool covers trapping chlorine and causing it to dissipate more rapidly.
6. In some cases, your chlorine levels might be too high, and this can cause your test kit reagents to bleach out, making it look like there’s no chlorine in your pool.

How to Test for High Chlorine Demand 

The quickest way to determine if your pool has high chlorine demand is by testing for free chlorine and total chlorine levels. Our Pool Test Kits can assist with this.

• Free chlorine is the active, disinfecting chlorine.
• Total chlorine is the combined amount of used and unused chlorine.

If these readings are significantly different, it indicates that your pool has a high chlorine demand. For example, a free chlorine level of 3 and total chlorine of 7 means chlorine is being used up too quickly to sanitise effectively.

Some recommended products within our Pool Test Kits that can be used to test for high chlorine demand:

• AquaChek 7 Test Strips (tests for free and total chlorine)
• AquaChek 4 in 1 Test Strips for Pool and Spa (tests for free chlorine)

Not sure how to test? Bring a sample to one of our stores across Australia for a FREE chlorine demand test. Our experts can help pinpoint the problem for you.

Solutions for High Chlorine Demand 

1. Partially Drain and Refill Your Pool

Sometimes, reducing the chlorine demand involves partially draining the pool and refilling it with fresh water. This dilutes the contaminants and allows chlorine to work more effectively. This is especially helpful after winter or periods of inactivity. For more guidance on this process, check out our pool water management tips here. 

2. Shock the Pool

Another method is to shock the pool with a high level of chlorine (20ppm or higher) or a non-chlorine oxidising shock to break the chlorine lock. This can help balance the free and total chlorine levels and allow the chlorine to disinfect properly again. Learn more about our pool shock products here.

3. Test Your Pool Water In Store

If you're unsure of your chlorine levels or the proper treatment method, bring a water sample to one of our stores. We have stores in Sydney, Canberra, Newcastle and Gold Coast, where our experts can conduct a FREE chlorine demand test and recommend the best course of action.

4. Book a Pool Technician Visit

With over 40 experienced technicians across Sydney, Canberra, Newcastle and Gold Coast, we can help get your pool back to perfect condition. Visit our Pool Service page and fill in the contact form to book a visit.

Preventing Future Chlorine Demand Issues

To prevent high chlorine demand from occurring, here are a few tips:

• Brush your pool walls to remove algae buildup. Our Stainless Steel Algae Brush is perfect for the job. Or you may prefer our Super Pool Broom.
• Keep your pool clean by regularly removing debris and cleaning the filter.
• Regularly test and balance your pool water and ensure your pH and chlorine stabiliser levels (Cyanuric Acid) are in the right range.
• Monitor salt levels, and make sure your salt levels are at the correct level for your specific salt chlorinator. This is generally between 3500ppm and 6000ppm, depending on your chlorinator.
• Run your Eco pump for the recommended hours for your size pool. Eco pumps, while energy-efficient, can sometimes run too slowly for adequate chlorine distribution. Get expert advice on the best pump settings for your pool by scheduling a visit from one of our 40+ pool technicians or visiting one of our stores.