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  • Writer's picturePool Protection Technologies

How To Raise Free Chlorine Levels In A Pool

Ever wondered how your drinking water stays clean and safe? Well, that's where free chlorine comes in. It's a powerful chemical compound used to keep our water free from harmful bacteria and other nasty stuff. You'll find it doing its job in public water treatment systems, swimming pools, and even spas. Free chlorine works by zapping away those pesky microorganisms that can make us sick, such as bacteria, viruses, and parasites. It's like a superhero for water, ensuring that we have clean and healthy H2O to drink and enjoy. So, the next time you take a refreshing sip of water or jump into a pool, thank free chlorine for keeping things clean and germ-free!

Maintaining proper chlorine levels in your pool is crucial for ensuring clean and healthy water. If your free chlorine levels are low, below 1 part per million (ppm), it's time to take action. Low chlorine levels can lead to algae growth and bacterial build-up, jeopardizing the safety and enjoyment of your pool. In this guide, we'll explore the common causes of low free chlorine and provide practical steps to raise those levels. So, let's dive in and learn how to keep your pool water crystal clear and sanitized!

Understanding Free Chlorine:

Before we delve into raising free chlorine levels, let's grasp its importance. Free chlorine refers to the available chlorine in your pool that actively sanitizes the water. It's the chlorine that hasn't been used up and is still ready to combat contaminants. Aim for free chlorine levels between 1 and 3 ppm to effectively kill harmful microorganisms. On the other hand, combined chlorine (chloramines) is chlorine that has already been used and is no longer effective. Keep the combined chlorine level below 0.5 ppm to prevent that distinct chlorine smell.

Picture Credit: Swim University

Causes of Low Free Chlorine Levels:

Several factors can contribute to chronically low free chlorine levels in your pool. Understanding these causes will help you address the issue effectively.

a) High Chlorine Demand:

A pool with a high bather load or excessive debris requires more chlorine to maintain proper sanitation. Increased contaminants lead to a higher chlorine demand. This is common after periods of neglect or heavy rainfall causing runoff into the pool.

b) Heavy Pool Use:

The more swimmers you have and the more frequently the pool is used, the more contaminants enter the water. Sunscreen, dirt, and oils from the skin all challenge the chlorine's effectiveness. Regularly shocking the pool after heavy use or parties helps maintain optimal chlorine levels.

c) Sunlight and Low Cyanuric Acid Levels:

If you use unstabilized chlorine (liquid chlorine or bleach), sunlight can rapidly degrade the chlorine. Cyanuric acid, also known as a chlorine stabilizer, protects the chlorine from the sun's UV rays. Test your cyanuric acid levels and use a stabilizer to prevent chlorine breakdown.

d) Very High Cyanuric Acid Levels:

Excessive cyanuric acid can weaken the sanitizing power of chlorine. If you use chlorine tablets, they can elevate cyanuric acid levels over time. Regularly test and maintain cyanuric acid within the recommended range of 30-50 ppm.

e) Increased Organic Contaminants:

Heavy rainstorms can introduce a significant amount of debris and organic contaminants into your pool, quickly depleting free chlorine. Clean debris promptly and shock the pool, especially after experiencing runoff.

f) Refilling the Pool with Fresh Water:

Adding fresh water can disrupt the pool's chemistry, diluting the existing pool chemicals, including chlorine. Adjust your pool chemicals accordingly after refilling.

g) Not Adding Enough Chlorine:

Low free chlorine levels may simply result from not adding enough chlorine regularly. Ensure proper chlorine addition and monitor the equipment, such as skimmers and floaters, to maintain consistent chlorine levels.

h) Not Enough Salt in Your Saltwater Pool:

If you have a saltwater pool, low chlorine levels could indicate insufficient salt content. Regularly test and maintain the appropriate salinity level while also inspecting the salt water generator for optimal functionality.

Steps to Raise Free Chlorine in Your Pool:

Now that we've identified the causes, let's explore practical steps to raise your free chlorine levels and restore water quality.

Step 1: Clean and Balance

Start by thoroughly cleaning your pool to remove any debris, leaves, or algae that may be consuming your chlorine. Use a skimmer net or vacuum to eliminate visible dirt and leaves from the water surface and bottom of the pool. Brush the pool walls and floor to dislodge any stubborn algae or buildup. Once the pool is clean, test the water to ensure proper pH, alkalinity, and cyanuric acid levels. Balancing these parameters sets the stage for effective chlorine treatment.

Picture Credit: Forbes

Step 2: Shock Your Pool

If your chlorine levels remain low after cleaning and balancing, it's time to shock your pool. Shocking involves adding a high concentration of chlorine to rapidly raise the free chlorine levels above the combined chlorine levels, effectively sanitizing the water. There are different types of chlorine shocks available, so choose the appropriate one for your pool.

For Traditional Chlorine Pool Owners:

Use calcium hypochlorite (cal-hypo) shock as it is a powerful chlorine shock that quickly raises free chlorine levels. Add the cal-hypo shock to your pool at night to minimize degradation from the sun's UV rays. Follow the manufacturer's instructions for the recommended dosage based on your pool's size. Allow at least 8 hours for the shock to work before swimming again. In cases of high chlorine demand, consider triple shocking the pool.

For Saltwater Pool Owners:

Use sodium dichlor shock specifically formulated for saltwater pools. This type of shock helps raise chlorine levels without causing scale buildup on the saltwater generator. However, be aware that it can also increase cyanuric acid (CYA) levels. If your pool already has high CYA levels, consider using liquid chlorine instead.

Step 3: Monitor and Adjust

After shocking the pool, regularly monitor the chlorine levels using test strips or a liquid testing kit. Aim for free chlorine levels between 1 and 3 ppm and ensure that the combined chlorine level remains below 0.5 ppm. If necessary, repeat the shock treatment or make smaller chlorine additions to maintain the desired levels.

Step 4: Address Other Chemical Imbalances

If your free chlorine levels continue to remain low despite shock treatments, check for other chemical imbalances. Fluctuations in pH or cyanuric acid levels can affect chlorine effectiveness. Adjust these parameters as needed to optimize chlorine performance. Remember, maintaining proper water balance is essential for chlorine to work efficiently.

Step 5: Seek Professional Help

If you've followed the above steps and still struggle to raise free chlorine levels, it may be time to consult a pool professional. They can conduct a comprehensive analysis of your pool's chemistry and recommend appropriate actions to restore chlorine balance.


Ensuring adequate free chlorine levels in your pool is vital for maintaining clean and safe water. By understanding the causes of low free chlorine and following the steps outlined above, you can effectively raise chlorine levels and prevent issues like algae growth and bacterial contamination. Regular testing, cleaning, and proper chemical balancing will help you enjoy a sparkling and healthy pool all season long. Remember, a well-maintained pool is a source of relaxation and fun for you and your family.

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