How Do I Fix Chlorine Demand and Chlorine Lock?

Are you having problems getting a sustained level of chlorine in your pool, despite regular maintenance and shocking? If so, your pool may have a chlorine demand problem.

How Chlorine Demand Occurs

Chlorine demand problem occurs when Free Chlorine is not available to sanitize the pool. What happens is most of the chlorine added to the water reacts with organic matter or other chemicals to form compounds called chloramines. Even though the total chlorine content in the pool is high, the Free Chlorine is consistently too low to sanitize. The cure usually involves adding large amounts of shock chemicals to the water to remove the chloramines, and then following up with routine shocking.

So what are chloramines?

Chloramines, also known as "combined chlorines," form when chlorine reacts with organic waste like sweat, saliva, and body oils in the pool. This creates the strong chlorine smell and reduces chlorine’s ability to sanitize the water. High chloramine levels often occur when a pool is left unattended or not properly cleaned before closing.

To prevent this, maintain proper chlorine levels daily and shock your pool weekly to replenish free chlorine. Regular cleaning and proper pool closure can also save time and effort in the long run. Environmental factors like heavy rainfall or certain household bleach products can also contribute to high chlorine demand. Additionally, if your municipality uses chloramines in drinking water, topping off your pool with tap water can increase chloramine levels, compounding the issue.

Fixing The Problem

How to Fix Chloramine Issues in Your Pool

To tackle chloramine buildup, start by testing and adjusting the pH of your pool to 7.4 - 7.6. Ensure your cyanuric acid (stabilizer) is between 30 ppm and 80 ppm for optimal chlorine efficiency.

Next, shock the pool at night when the sun won't affect the chlorine. Use 3 lbs. of shock for every 10,000 gallons of water. For a 21,000-gallon pool, this means adding 9 lbs. of pool shock.

Check the chlorine levels the following day and continue this process until your chlorine residual reaches 1.0 - 3.0 ppm. This is the ideal range for effective sanitation. Regular water testing and shocking will help prevent future issues.

Finally, ignore the term "chlorine lock"—it's a myth. Chlorine lock suggests that excessive cyanuric acid causes chlorine to stop working, but there's no scientific evidence to support this. Chlorine demand is a real issue, but chlorine lock is just a sales pitch.

Have a question about using the right chemicals for your pool?  Feel free to send us a message here.