Causes Of Swimming Pool Chlorine Loss & The Best Ways To Prevent It

One of the greatest achievements a pool owner probably has is mastering the water pool chemistry. Balancing the water with the correct amount of chlorine to keep it safe and clean requires the right knowledge, skills, and a bunch of patience. At this point, many pool owners get frustrated as the more they try to keep the water clean, the more the chlorine level decreases. While others have already attempted to drain and refill the water, some pool owners seek for an explanation of how the pool’s chlorine demand works.

If the water test results indicate a low level of chlorine when you just recently sanitized it, then you are losing them. If that is not corrected immediately, then more money and effort will go to waste. Chlorine sanitization should not take more than 2x per week. The causes of swimming pool chlorine loss and the effective ways to prevent it are two of the most talk-about pool concerns, which this article will discuss. 

Understanding the Root Cause

Learning the reasons why and how a swimming pool loses its chlorine is the first step to prevent it. Adding chlorine to the water for about 1-2x a week is rational and could only mean it is fulfilling its part in sanitizing the water, but needing to add more than that requires attention. The reasons why the chlorine level drops faster vary from things that are in and the situation around it. Here are some of the common causes:

1. Water Contamination – Highly contaminated water affects the level of chlorine. If humans have antibodies that protect them from various diseases, the pool water must have chlorine to act like neutralizers. These neutralizers will combat unwanted contaminants, whether it is organic or inorganic. As a result, the chlorine level drops, but it should gradually decrease.

If you notice that the chlorine drops faster, you need to test the status of the water. Analyze the level of water contamination, making the chlorine to dissipate. Some of the things that can pollute the water are:

  • Fallen leaves and twigs
  • Insects
  • Droppings from birds
  • Algae and microorganism build-up
  • Chemicals contaminants from lotion, shampoos, and soaps
  • Skin tissue and body oils, as well as makeups
  • Liquids excreted by users like sweat
  • Contamination from swimwear

The chemical reaction of chlorine with water is to break into several properties. They can either become hypochlorite ion or hypochlorous acid. When any of these pollutants contaminate the water, the chlorine will attack them, and soon they will oxidize in the process.

2. The Effects of Sun’s UV Rays – Although the presence of the sun can make water a little warmer, it has adverse effects on chlorine. As soon as the sunlight touches the water, the hypochlorite ion on chlorine splits apart and oxidizes without the chance of performing its purpose. It is the exact reason why some pool owners use cyanuric acid as a chlorine neutralizer. It acts like a protective shield that makes the chlorine more active and UV rays resistant, for a limited time until the CYA or cyanuric acid evaporates. Without this stabilizer, the water that gets direct sunlight can lose up to 90% of the chlorine in less than 3 hours. 

3. High Temperature – The hot temperature is another cause of chlorine loss. Meaning, even though the sunlight does not hit the water directly, for as long as it is up and its rays are reflecting everywhere, producing heat temperature to the atmosphere, it will still make the water evaporate.

Additionally, bacteria are commonly known to adapt well to a warm environment. When the water gets warmed by the sun or by the steamy temperature, it will be more comfortable not only for humans but also for microorganisms. The result, they will multiply faster. 

4. Adverse Effect of Cyanuric Acid – In case you are not familiar, there are two types of chlorine, unstabilized and stabilized. The unstabilized chlorine is commonly used in indoor pools since there is no need for sun protection. The stabilized chlorine has CYA or Cyanuric Acid. The CYA has its pros and cons. They may work effectively like a sunscreen to chlorine, but they also make it less capable of sanitizing the water, causing chlorine lock. It the term used when the level of CYA gets too high, and the chlorine can no longer do its task, leaving you with unsanitized water.

You may quickly identify if the pool has a high amount of CYA. It produces a strong smell of bleach, and that is not because the chlorine has exceeded the limit amount, but it is otherwise. The odor comes from a chemical substance called chloramines, a product of poor water treatment.

5. Badly Treated Water –  Chemically unstable water is another reason why chlorine loses its ability to disinfect.  If the water is imbalanced, either too high on alkaline or acid, the chlorine will not work, and most likely, it will just sit at the bottom of the pool. A common sign that your pool is out of balance is when the water still appears to be cloudy after chlorine sanitation.

Every chemical that the pool requires has a recommended amount based on the volume of water and other chemicals that you need to add. Maintaining chemically balanced water can be challenging, but it can save you from future troubles and expenses.

6. Rainwater Vs. Pool Water– The rainwater, either falling directly or through run-offs, can make the pool acid level shoot up. In short, a messed-up water pool chemistry. Aside from that, the rainwater may contain dirt and bacteria that will pollute the pool.

Imagine how complex these will be for chlorine – unbalanced, contaminated water. The chlorine will become very active on water with a low level of pH, causing them to get consumed up immediately.

7. Uses and Users – Regular use of pool and users can also be significant factors why a pool loses chlorine. As mentioned earlier, when a human discharges liquid, they add up as water pollutants. It triggers the chlorine to sanitize sweat, pee, and body oils. Furthermore, the human skin tissue, hair, along with many other things that a person could bring into the water will serve as an enemy to the chlorine.

If the swimming pool is under regular usage, then there is a need to increase the amount of chlorine, which should be about 1-3 parts per million. Moreover, advising the users to wear proper swimming attire and taking showers before hitting the pool will help a lot.

All these and more contribute to the cause of pool chlorine loss, and explaining them can help better understand how to avoid them. There may be no way to stop rainfall and high temperatures, but there are ways to minimize their effect on chlorine. The next part of this article will guide you on how to limit or have control over chlorine loss.

Proper Pool Sanitation to Avoid Chlorine Loss

As you may remember, the top cause of pool chlorine loss is highly-contaminated water. As soon as the chlorine dive into the water, it will start to disinfect. When there’s too much to clean, the chlorine will get used up instantly.

According to, weekly pool maintenance and water sanitation can help to slow down the chlorine consumption.

  1. Help the chlorine to clean the water by skimming out the dried leaves, twigs, and insects. Let the chlorine handle the microorganism and bacteria, while you deal with those that are visible to human eyes.
  2. Regularly scrub the pool surface, wall, and stairs can prevent algae and bacteria build-up. To reach the bottom and far sides, attach the brush to a telescopic pole. Focus on areas that have no to little water circulation.
  3. Collect the dirt and visible debris using a pool vacuum. Allow the debris to settle and slowly move the vacuum head. Try not to make any rough movement as it may cause the particles to float again.
  4. Check if the filters are clean. Backwash it if you notice residues. Also, inspect if the pump is functioning well.
  5. Test the water by using chlorine level test kits. To get the most accurate result, try to dip the tester at least 20 inches deep. Make sure that the level of water reached the “fill line” level. Add the required amount of solution, mix, wait for a few seconds, then compare the color with the equivalent level. 
  6. Oxidize or Shock the Pool. Never forget to put on your protective gear whenever you apply chemicals to your pool. Pool shock is another form of water treatment to use. To apply, add the substance in a bucket of water and then mix it. Next, distribute it evenly by pouring the mixture to different sides of the pool. 
  7. Leave the pool pump running for 8 hours. Note that the chemical can be too strong, so you need to make everyone aware, especially kids, to stay out of the pool for the meantime. It is a long wait, which is why most pool owners suggest doing the pool shock at night.
  8. Re-testing the water after the pool shock treatment is necessary. It will allow you to get the actual chlorine level reading. Adjust the level by adding more then wait for 2-4 hours to take another test. Remember that adjusting the chlorine by adding more is better than exceeding the recommended level. 

Solar Cover as an Alternative Pool Protection

Other than regular maintenance and cleaning, there are other methods to prevent chlorine loss. Since chlorine dissipates in the presence of the UV rays, many pool experts suggest the use of a pool cover. It offers a lot of benefits to a swimming pool, although it also has some drawbacks. To give a few:


  • It covers the pool from direct sunlight, allowing you to save 30%-50% of the water from evaporation and chemical usage by up to 40%
  • It absorbs and keeps the heat to make the water warmer, thus, allowing you to save on power or gas consumption from a water heater.
  • It shields the water from debris and other pollutants.
  • It protects the water from both high and cold temperatures during the night.


  • Putting the cover on and off the pool requires effort
  • The collected leaves and debris on top fall may tend to fall into the water when removing the cover. 
  • It decreases the pool’s aesthetic appeal.

Timeframes to Remember

Maintaining a pool is an endless cycle, yet the result is rewarding. There’s a lot of things to remember and do. Pool sanitation, water testing, equipment inspection, and such can help improve the quality of water if, and only if, you do it frequently. To further help, list down this timeframe, so you won’t forget:

  • Test the pH level at least 2x a week.
  • Do the alkalinity test every 1st and 3rd week.
  • Test the chlorine level every 2nd and 4th week.
  • Perform a CYA and calcium hardness test 2x in each season.
  • Complete a total dissolved solids test at least 1-2x a month.

Conclusion and Recommendation

It takes a lot to get a full grasp of what pool needs. Uncovering its demand for chlorine may include learning the proper ways to maintain it, as well as understanding the language of pool chemistry. There is no need to memorize every chemical’s function and purpose to manage a pool. As long as you do the basic requirement of sanitizing and follow the guidelines, it is possible to achieve chemically balanced yet safe water.

Pool owners have these feeling of satisfaction whenever they achieve well-balanced water. To further confirm the consistency and safety of your water, have it checked by the experts who can use a more advanced method of chlorine level testing or bring a water sample to a reputable pool service provider for professional screening. That way, you will know whether you are doing it right or if you need to learn more.