How to Use Sodium Thiosulfate in Your Pool

Written by Michael Dean
September 20, 2023

sodium thiosulfate in swimming pool

If you are a pool owner, chances are you’ve used chlorine. Chlorine is the most popular chemical used in pools to keep them sparkling clean. However, it is imperative that you constantly monitor your chlorine levels because if the levels are too high, you risk irritating the eyes and skin of swimmers. But mistakes happen, and when they do, sodium thiosulfate is your best friend! Sodium thiosulfate can help lower chlorine levels back to the recommended range.

In this article, I will cover the common causes of high chlorine levels in pools and how sodium thiosulfate can help regulate it.

Main Takeaways

  • You can use sodium thiosulfate as a chlorine neutralizer to help control and deplete your chlorine levels if they are too high. 
  • Sodium thiosulfate reacts with chlorine, converting it into a harmless compound, resulting in a cleaner and more comfortable swimming environment.
  • When using sodium thiosulfate in your pool, test the chlorine levels, calculate the appropriate dosage, add the chemical, and adjust the pH if necessary.
  • Alternatives to sodium thiosulfate include sodium sulfite, ascorbic acid, calcium thiosulfate, and hydrogen peroxide. Other alternatives include simply waiting or doing a partial drain and refill.

What is Sodium Thiosulfate for Pools?

Sodium thiosulfate (Na2S2O3) is an inorganic sodium compound made of sodium and thiosulfate ions. It is a crystalline compound that readily dissolves in water, making it suitable for pool treatment. Sodium thiosulfate reacts with chlorine, converting it into a harmless, non-irritating compound. Its ability to dissolve and react quickly makes sodium thiosulfate a very effective neutralizer for pools. And on the plus side, it’s pretty affordable as well!

How to Use Sodium Thiosulfate in Your Pool

Everyone who owns a pool has accidentally added too much chlorine at some point. Be it because you simply miscalculated or you continued adding stabilized chlorine that does not easily dissipate, it is a relatively common mistake to overdose your pool with chlorine. Using sodium thiosulfate is the easiest way to lower your chlorine levels quickly.

Here is a step-by-step guide to help you effectively add sodium thiosulfate to your pool.

Step 1: Test Chlorine Levels

First, check your chlorine levels using a reliable pool test kit before adding sodium thiosulfate. Your chlorine levels should be between 2 to 4 parts per million (ppm). 

Check out my pool chlorine calculator for more info on testing your pool and determining how much chlorine to add to your pool in the first place.

Step 2: Determine How Much Sodium Thiosulfate to Add

Typically, you’ll need to add 2 ounces of sodium thiosulfate for every 10,000 gallons in your pool to reduce the chlorine levels by 1 ppm. However, it is essential to consult the manufacturer’s instructions and adjust the dosage based on your pool size and chlorine levels.

Step 3: Pre-Dissolve the Mixture

Once you have determined how much you need, add the required dosage of sodium thiosulfate to your pool. Pre-dissolve the required dosage in a container.

Step 4: Pour the Pre-Dissolved Mixture into the Pool

Next, pour the dissolved sodium thiosulfate into the pool and leave the pump on, allowing it to circulate for a few hours.

Now, go make yourself a drink, relax by your pool, and in 2-3 hours, you should be good to go!

Step 5: Test Your Chemical Levels

The final step is to test your chlorine levels again after a few hours. If the chlorine levels are still high, add more sodium thiosulfate and repeat the process again. You should also test your pH levels and adjust as necessary because sodium thiosulfate has a low pH.

Pros and Cons of Sodium Thiosulfate for Pools

As you can probably already see, sodium thiosulfate is an excellent way to lower chlorine levels in your pool, but nothing comes without any downsides. Here are some pros and cons of using sodium thiosulfate in a swimming pool.


  • Effective chlorine neutralizer: The biggest selling point for sodium thiosulfate is that it is a reliable and highly effective way to lower chlorine levels in your swimming pool. It rapidly reacts with chlorine, converting it into a harmless compound.
  • Cost-effective solution: Sodium thiosulfate is also relatively inexpensive, so if you add too much chlorine to your pool, you can rest assured that it won’t cost you much!
  • Immediate chlorine reduction: Sodium thiosulfate works quickly, beginning to neutralize chlorine upon adding it to your pool. This makes it a super convenient option for lowering chlorine in a pinch.


  • pH level reduction: Sodium thiosulfate is an acidic compound that can lower the pool water’s pH level. Pool owners must monitor the pH levels after using sodium thiosulfate and make necessary adjustments using pH increasers such as sodium bicarbonate or soda ash.
  • You can get similar results by giving it some time: While sodium thiosulfate is a good solution if you need to reduce your chlorine levels quickly, the best way is to let the chlorine dissipate in the sun naturally.

Alternatives to Sodium Thiosulfate for Pools

While sodium thiosulfate is a commonly used chlorine neutralizer in pools, alternative methods are available for controlling chlorine levels and maintaining water quality. Here are a few of the best alternatives you can consider.

Sodium Sulfite

Sodium sulfite (Na2SO3) is a common alternative to sodium thiosulfate for neutralizing chlorine in pools. Sodium sulfite can effectively decrease chlorine levels by 1 ppm by adding 2.4 oz. per 10,000 gallons of water. It is an excellent alternative to sodium thiosulfate. However, it’s essential to handle sodium sulfite with caution and use proper personal protection equipment due to its moderate toxicity.

Ascorbic Acid

Another option is ascorbic acid (Vitamin C), which can neutralize chlorine without affecting the pool’s pH. However, ascorbic acid is much more expensive, so sodium thiosulfate is a more cost-efficient solution.

Calcium Thiosulfate

Calcium thiosulfate is another alternative to sodium thiosulfate for controlling pool chlorine levels. It works similarly, converting chlorine into a harmless compound. Calcium thiosulfate is often used along with calcium hypochlorite, a common pool sanitizer, to regulate chlorine levels effectively.

Hydrogen Peroxide

Hydrogen peroxide (H2O2) is a powerful oxidizing agent that effectively neutralizes chlorine. Make sure to use hydrogen peroxide specifically made for pools instead of for general household use. And for maximum effectiveness, ensure your pool’s pH is higher than 7.

Time and Sun

Ready for the cheapest and most natural way to get rid of high chlorine levels? Simply let the sun work its magic!

Chlorine naturally dissipates under the sun’s UV rays, so if you add too much chlorine, you can simply wait for the sun to balance it for you. UV rays can break down chlorine in your pool by more than 90% in a matter of hours.

Partial Drain and Refill

Another way to lower high chlorine levels in your pool without adding any chemicals is to partially drain and refill your pool. That said, refilling your pool can be time-consuming and costly, so I wouldn’t recommend this unless your pool has WAY too much chlorine.

Causes of High Chlorine Levels in Your Pool

So, what causes high chlorine levels? Knowing the causes is the first step to maintaining your chlorine levels. Armed with this knowledge, you may be able to avoid using sodium thiosulfate in the first place!

Adding Too Much Chlorine

Of course, the main cause of high chlorine levels in your pool is simply overusing the chlorine. Always follow the manufacturer’s instructions and guidelines for how much chlorine to add to your pool to avoid over-chlorination. You may be dealing with high chlorine levels due to a simple slip-up or due to buildup over time.

Always, always test the pool before adding more chemicals, including chlorine.

Inadequate Dilution

Improper dilution or uneven distribution of chlorine in the pool can result in certain areas of the pool with high chlorine concentrations. If you use chlorine tablets, make sure your chlorinator is distributing the chlorine properly, and ensure your filter is run for at least 8 hours a day to make sure all the chemicals properly circulate throughout the whole pool. And finally, when you shock the pool, run the filter continuously for at least 8 to 10 hours.

Lack of Pool Maintenance

A major part of pool maintenance is simply looking after your pool equipment and testing your water. If you neglect your filter and pump, the water may not be circulating properly, which can cause the water to be hypersaturated with chlorine in certain areas. 

pH Imbalance

An imbalanced pH level can also affect chlorine’s effectiveness. In fact, as pH goes up, the germ-killing power of chlorine diminishes. This can cause a higher chlorine demand, eventually causing your pool to be over-chlorinated. To avoid this regularly, test and adjust the pH level of your pool water.

Risks of Over-Chlorination

Over-chlorination, or excessively high chlorine levels in a pool, can pose several risks. You have to be aware of these potential issues to maintain a safe swimming environment.

Skin and Eye Irritation

Elevated chlorine levels can cause skin dryness, itchiness, and irritation. Swimmers may experience redness, rashes, or even chemical burns on their skin. Furthermore, swimmers’ eyes may also become red, itchy, and irritated, leading to discomfort and potential vision problems.

Respiratory Problems

Breathing in chlorinated water vapor or mist, especially in indoor pools, can irritate your respiratory system. This can result in coughing, wheezing, shortness of breath, and exacerbation of pre-existing respiratory conditions such as asthma.

Discomfort and Odors

Because of all the above reasons, you can see that high chlorine levels can create an unpleasant swimming experience overall. Swimmers may notice a strong chemical smell that can be overpowering and bothersome. The chlorine odor can also cling to hair and swimwear. Plus, chlorine can even cause chemical reactions on your hair and swimsuit, causing damage and discoloration.

Damage to Pool Equipment

Additionally, excessive chlorine can corrode pool equipment and infrastructure. When the levels are high, it may cause deterioration of metal fixtures, pipes, and pump parts, leading to costly repairs and replacements. Over time, this can compromise the integrity of the whole pool system, which is the last thing you’ll want!

Need Some Maintenance Help?

Send me a message! I can answer any of your pool maintenance, equipment, or other questions.

Frequently Asked Questions

Are there any alternatives to chlorine?

Yes, there are alternatives to chlorine for pool sanitation. Some alternatives include bromine, ozone, UV systems, and biguanide. These alternatives provide effective pool sanitation methods while reducing the reliance on chlorine.

How long does it take for sodium thiosulfate to work?

Sodium thiosulfate will technically neutralize the chlorine immediately, making it an excellent choice for lowering chlorine levels if you want it lowered ASAP. However, with that said, you still need to allow some time for the sodium thiosulfate to circulate the whole pool, which may take a couple of hours.

Can you put too much sodium thiosulfate in the pool?

While high levels of sodium thiosulfate are generally not toxic, it is still important to exercise caution and not overuse it. Adding excessive amounts of sodium thiosulfate can also lower the pH of the pool water. Furthermore, too much sodium thiosulfate can cause problems if you later want to increase the chlorine level in your pool. And if you don’t have enough chlorine, you’re inviting a whole host of issues, such as algae, to attack your swimming pool.

Does sodium thiosulfate lower pH?

Sodium thiosulfate is an acidic compound that can decrease the pH of your pool. Therefore, make sure to monitor the pH levels after using sodium thiosulfate. If needed, you can make necessary adjustments using baking soda or soda ash to maintain the desired pH range of 7.2 to 7.6.

Maintain Your Chlorine Level Between 2 to 4 ppm

Sodium thiosulfate is a great and cheap way to lower your chlorine levels if they are too high and you can’t wait for the chlorine to dissipate on its own. Always make sure to test the pool before you jump in, as too much chlorine can be uncomfortable and irritating, while too little chlorine means your pool is not properly sanitized.

Do you have any more questions about sodium thiosulfate or other pool chemicals? Let me know, as I’m happy to help.

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