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3 Simple Ways to Raise Free Chlorine Levels in a Pool


Maintaining the clarity and balance of pool water is no easy task. This is because, in terms of water chemistry, you must pay attention to many different factors.

While most people are aware of the importance of chlorine and shock in preserving pool water quality, there are other essential pool chemical components that are often overlooked. One of these is free chlorine low.

Part 1. What Is Free Chlorine?

Free chlorine is a key component in pool water quality. It exists in the form of chlorine ions (Cl-) in swimming pool water. The primary function of free chlorine is to eliminate microorganisms, bacteria, and algae present in the water, ensuring clean and safe water quality. It is the primary form of chlorine used for disinfection in swimming pools as it directly reacts with contaminants and effectively eliminates them.


The ideal range for free chlorine levels typically falls between 1 to 3 ppm (parts per million). This range ensures that there is enough chlorine in the water to eliminate microorganisms while avoiding excessively high chlorine concentrations that could have adverse effects on pool water quality and equipment.

In contrast to free chlorine, combined chlorine (also known as chloramines) is chlorine that has already been used to combat contaminants in the water, but it has completed the disinfection process and no longer possesses sanitizing capabilities. The concentration of combined chlorine should not exceed 0.5 ppm. Elevated levels of combined chlorine typically indicate the presence of chloramines, which can lead to poor water quality and the release of the characteristic chlorine odor.

Tips: If you want to learn more about the difference between free chlorine and total chlorine, you can click here.

Part 2. Reasons for Low Free Chlorine Levels

Several factors can contribute to free chlorine low levels:

a. Pool Water Contaminants:

Organic pollutants such as leaves, debris, and other organic matter can consume free chlorine as chlorine reacts with these pollutants.

Inorganic contaminants, such as sunscreen, soap, hair products, and more, can also reduce free chlorine levels as they introduce external chemicals into the water.

Solution: Regularly remove organic and inorganic contaminants from the water, including skimming debris, brushing pool walls, and vacuuming. Perform pool shock treatments weekly to clear accumulated contaminants and adjust chlorine levels as needed.

b. UV Exposure from Sunlight:

Exposure to ultraviolet (UV) rays from the sun can lead to the breakdown of free chlorine, resulting in a natural decrease in free chlorine levels, especially in outdoor pools.

Solution: Use a solar pool cover to reduce the impact of UV rays, especially when the pool is not in use.

c. Water Chemistry Imbalance:

If the pH, alkalinity, or other water chemistry parameters of the pool water are not within the appropriate range, free chlorine may not work effectively, allowing microorganisms and algae to thrive and consume free chlorine rapidly.

Solution: Regularly test and adjust the pool water's pH (7.2-7.8), alkalinity (80-120 ppm), and other water chemistry parameters to ensure they are within the appropriate range. Specific pH and alkalinity ranges may vary depending on the region and pool type.

d. High Bather Load:

Large-scale pool events, such as pool parties or a high volume of swimmers, can introduce more contaminants into the water, leading to rapid consumption of free chlorine.

Solution: Perform shock treatments on the pool after significant events to clear contaminants, and regularly monitor free chlorine levels to ensure clean and safe water quality.

Part 3. How to Increase Free Chlorine Levels

a. Use Trichlorine Tablets:

  • Trichlorine is a commonly used chlorine disinfectant, especially for outdoor pools.
  • It is cost-effective but should be used with caution to avoid skin irritation.
  • Trichlorine tablets dissolve slowly and are suitable for use with chlorine feeders.

Note that trichlorine tablets may lower the pool's pH, so you may need to add sodium bicarbonate or other alkaline substances to balance the pH.

b. Use Dichlor Granules:

  • Dichlor granules are fast-acting and do not significantly affect pH or alkalinity.
  • They are suitable for quickly increasing free chlorine levels, such as before pool gatherings.

However, they are not suitable for use with chlorine feeders, floaters, or dispensers due to their fast dissolution rate. Additionally, using dichlor can increase cyanuric acid (CYA) levels, so consider other options if you are already dealing with high CYA levels, you can use liquid chlorine.

c. Chlorine Shock Treatment:

Chlorine shock treatment can be used to rapidly increase free chlorine levels and is suitable for situations where a significant increase in chlorine content is required.

Chlorine shock can quickly boost free chlorine levels, while non-chlorine shock reduces combined chlorine but does not increase free chlorine levels. Chlorine shock treatment should only be used when an increase of at least 10 ppm is needed.

Part 4. FAQs

a. Does a Free Chlorine Shock Increase Free Chlorine Levels?

Yes, pool shock treatments typically involve adding chlorine or non-chlorine chemicals to increase free chlorine levels and eliminate contaminants.

b. Is it Safe to Swim in Water Without Free Chlorine?

Swimming in water without free chlorine is unsafe, as it increases the risk of waterborne diseases and uncontrolled algae growth, making the pool unattractive for swimming. Therefore, maintaining an appropriate level of free chlorine is crucial for maintaining clean and safe pool water quality.

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