How to Lower Free Chlorine

If you shock the pool too close to activity time and guests are coming but the Chlorine residual level is still too high, there are a few things that you can do to reduce it and bring it down faster to a safer level before those guests arrive and want to swim. How do you lower Free chlorine?

  • Let filter run
  • Pull pool tablets from floaters
  • Scrub sides of walls with a long handle brush to agitate pool H2O
  • Add a Chlorine Neutralizer like
    Sodium Thiosulfate or Hydrogen Peroxide
  • Add H2O to dilute the pool
  • CL levels of 6 ppm or higher are unsafe.
  • Repeat until residual is safe to swim in approx. 5 ppm

Pools will naturally gas-off chlorine from the surface, and very high levels can irritate airways and lungs when inhaled for prolonged periods, especially indoor pools where there is no way for that gas to escape. Sometimes Public pools at campsites or Hotels will bump their free Chlorine residual up to 5 ppm in the morning in anticipation of expecting a crowd for the day.


How to Lower Free Chlorine


Chlorine is added to the pool water to kill germs. But it does not work right away. If used properly, free chlorine can kill most germs within a few minutes. CDC recommends pH 7.2–7.8 and a free chlorine concentration of at least 1 ppm in pools and at least 3 ppm in hot tubs/spas.

Normal pool-free chlorine levels are usually around 1.0 ppm to 3.0 ppm, depending on the level of stabilizer in the swimming water. If your pool water is much higher than that and you are spending a lot of time exposed to it, then chlorine could have some effect on you even at these lower concentrations.


Chlorine Levels for Swimming Pool Water


The Association of Pool and Spa Professionals recommends free chlorine levels be kept between 2.0 and 4.0 ppm.

The Centers for Disease Control recommends free Chl. level stay above 1 ppm in pools and 3 ppm in hot tubs. The easiest way to check your chlorine level is with test strips. Free chlorine is the amount of chlorine freely available to kill bacteria and other contaminants.

The recommended level of combined chlorine in your pool is no more than 0.2 ppm. The combined chlorine level in your pool or chloramines is the portion of chlorine level that has reacted with the pool water and microorganisms contained in it. It is a temporary form of chlorine that should be eliminated if there is enough free chlorine in the pool water to continue killing contaminates.

Too much-combined chlorine in your pool (more than 0.5 ppm) means that there is not enough free chlorine available to kill all the contaminants. When the combined chlorine level in the pool reaches these levels, it is recognized by a chlorine smell. The pool water may cause skin and eye irritation, be harmful to swim in due to bacteria, and may allow algae to form. Adding more chlorine to your pool won’t help.

Reduce Chlorine in Pool Water


Be on the safe easy side. If you decide to shock your swimming pool with chlorine, then the best time to do that is the night before you are planning to use it. This is for a couple of different reasons.

When the free Chlorine Residual level in your pool climbs above 5-6 ppm, it can cause skin and eye irritation. Just above the waterline in your pool, the free chlorine turns to gas from the agitation of the pool water. Operate your pool with low chlorine residuals but pay attention to Free Chlorine and Total Chlorine levels that will dictate the disinfecting power of the chlorine in your pool.

Be on the safe side. If you decide to shock your swimming pool then the best time to do that is the night before you are planning to use it. This is for a couple of different reasons. When the free Chlorine residual in the pool climbs above 5-6 ppm it can cause skin and eye irritation. Just above the waterline, the free chlorine turns to gas from the agitation of the water.

Can Chlorine Level Go Down by Themselves in Pools


Over time yes. Chlorine will burn itself off naturally.  Depending on how hot it is and how high your chlorine levels are will determine the amount of time needed.  It could be quick or it could take a few days. 

The chlorine gas moves from the pool water to the air. This may cause some breathing problems, so be on the safe side and wait until the Chlorine levels are lowered and retest. When it gets below 5 ppm it will be safe. It will naturally when:

  1. The Sun starts to burn off Chlorine Residual-the UV rays and heat from the sun reduce chlorine.
  2. Activity in the pool depletes chlorine residual- the more splashing and pool movement the better
  3. Turn off your chlorinator 
  4. Dilute the pool with water-add more water to lower chlorine levels

When you super-chlorinate or Shock your pool you are looking to get your chlorine residual at high levels of approx. 10ppm and above and with a normal tester you’ll get an orange or red-colored reading that won’t be readable but you can safely assume the reading is high enough to work.


The same goes for Strip Testers normally 10 is the highest you will see. You can dilute the sample with half pool water and half drinking water and just multiply it by two. Always use a reliable kit and fresh reagents (check expiration dates on bottles) before Testing Pool Water.

Lower High Chlorine with Sodium Thiosulfate


After you shock the pool which can bring maximum levels of  Free Chlorine Residual, it will take some time to lower the free Chlorine levels back to where it’s safe to swim in. Bringing that residual back to a normal reading of 1 to 3 ppm will happen eventually when the sun starts to burn it off.

If you don’t have the time then there are a few ways how to lower and reduce free and Chlorine levels to get the chlorine into a gaseous form to leave the pool water a little faster. Shake it Up!

  • Turn the filter on and start moving the pool water around. This will help agitate the water and release chlorine in gas form
  • Scrub the sides of the walls of the swimming pool as this really helps move the water around and you’ll even smell the Chlorine coming out into the air around the pool area.
  • Pull the pool tablets from the floaters
  • Add a Chlorine Neutralizer like Sodium Thiosulfate
  • Turn the Heater On-Temperature can indirectly affect the chlorine levels of the pool water. An increase in temperature causes bacteria to proliferate, which use more of chlorine.
  • Does baking soda neutralize chlorine?  NO- it will raise the alkalinity in your pool water but will not neutralize the high-free chlorine in your pool.


Other ways of reducing chlorine are to add chemicals like Sodium Thiosulfate which is sold in Pool Supply stores will deplete the extra Chlorine in a little time. Calibrate the dosage and amount needed to lower the free chlorine level. Follow directions for best results.

Initial Dosage: 2 oz. per 10,000 gallons will lower free chlorine level by 1 ppm

These inexpensive chlorine neutralizers work so well they bring your water to clarity and make it crystal clear. Follow the instructions for the best possible results.

Typically, chlorine neutralizer for swimming pools contains sodium thiosulfate which acts to quickly lower pool-free chlorine concentrations. Nothing turns swimmers away faster than the strong chemical effects that are caused by chlorine.

Neutralizers like Sodium Thiosulfate which is the active ingredient will work with Chlorine or Bromine. This neutralizer will work fast and with little of it so don’t overdo it just follow directions.

For Sodium Thiosulfate, add about a cup (8 oz) of the dry white crystals per 5,000 gallons of pool water, or about 1 oz per 1000 gallons to reduce chlorine levels

to lower pool chlorine by 10 ppm. Check your pool water pH and adjust to within label instructions, and add directly to the pool or spa. The Sodium Thiosulfate that you add to the swimming pool will lower free chlorine and then dissipate from most pools usually within a few days.


More options for removing free Chlorine & Lower Chlorine Levels:

  1. Remove free chlorine naturally with sunlight, aeration, and agitation of the water.
  2. Add Sodium Thiosulfate,  Chlorine Neutralizer, for instant reduction of high-free chlorine.
  3. Add Ascorbic Acid-Vitamin C is most often used as a stain remover for swimming pools, but it can be used to cut down high chlorine levels, too. A 10 oz. dose per 10,000 gallons of pool water will lower chlorine levels by about 3.0 ppm.
  4. Add Hydrogen Peroxidehelps to break down and lower chlorine and works best with pH levels of 7.0 or higher. Use 7 oz. of Aqua Silk Oxidizer (27% hydrogen peroxide formula) per 10,000 gallons of pool water to lower chlorine level by 3.0 ppm.
  5. For Hot Tubs & Spas and smaller bodies of water, use 1 oz. of 3% drug store grade hydrogen peroxide per 100 gallons of spa water to reduce chlorine (or bromine) levels by about 5 ppm. Remember that pH levels will drop after an effective hydrogen peroxide treatment. Be sure to rebalance your water when done.

Too much free chlorine can lead to serious problems in your pool as it can damage pool equipment and bleach hair and swimwear on people in the pool. Free chlorine degrades when exposed to ultraviolet light, so the solution may be as simple as halting the addition of chlorine to the water and leaving your pool uncovered and unused on a sunny day. On a clear day, direct sunlight will remove up to 90% of the free chlorine in your pool in as little as two or three hours.


Can you Swim in a Pool with Combined Chlorine?

Combined chlorine or Chloramines an ineffective form of sanitizer recognized by an unpleasant sour chlorine smell irritating the eyes and skin of swimmers that are in the pool water close to the surface, prolonged exposure to combined chlorine can lead to asthma, allergies, and other health issues. ………………………………………………….. Read more

How to Reduce Free Chlorine in Saltwater Pool


For saltwater pools, you can take several steps if you know how to lower chlorine levels:

  1. Use the Sunshine– lowers acts as a neutralizer in pools- A quick and easy helpful way to lower the chlorine levels in pool water is to take advantage of a warm, sunny day
  2. Heat the Pool Water- to reduce the chlorine level in pools and lower alkalinity and pH
  3. Dilute the Pool-to reduce chlorine levels-turn on the filter to waste and pump water out-refill to proper levels chlorine levels in pool water
  4. Use Hydrogen Peroxide– a chlorine neutralizer for pool water and hot tubs to reduce high chlorine levels in the system 
  5. Sodium Thiosulfate chlorine neutralizer– just as in freshwater pools, Sodium thiosulfate products are an easy, affordable alternative to pre-formulated chlorine-neutralizing products for swimming pools. The amount you need to lower high chlorine depends on the number of gallons of water in your pool system or spa/hot tub and the initial chlorine level. 
  6. Add Ascorbic Acid, a.k.a. Vitamin C, to remove chlorine.
  7. Remove chlorine naturally with sunlight, aeration, and agitation of the water.


According to EPA Chlorine and bromine are unique in their ability to provide disinfection. EPA requires all US facilities that treat water to maintain a chlorine residual of no more than 4 parts per million, whether chlorine is used as a primary disinfectant or not. Chlorine gas is a respiratory irritant that the human nose can detect at very low levels (0.2-0.4 parts per million in air. Although Chlorine is necessary it’s also dangerous.


Symptoms of Pool Chlorine Poisoning


When adjusting chlorine levels in a chlorinated pool and too much is added to the pool water, you must lower the chlorine level to a safe reading. A safe pool can become a pit of harmful chemicals. In fact, over-chlorinated pools threaten swimmers’ health in two ways.

First, contact with the skin can cause irritation, similar to a burning sensation. Reduce the pool chlorine levels to an acceptable range, run pumps to agitate pool or spa water, and stop the chlorine source.

When a pool’s chlorine level or hot tub is super-chlorinated, the chlorine level is raised to between 10 ppm and 20 ppm. These chlorine levels are unsafe to swim in and can burn or irritate your skin and eyes.

Find a way to reduce chlorine to less dangerous levels. Start at the source, chlorine generator, chlorine tablets, run pumps, and chlorination system, shut down the pool, and pull tablets. 

As is the case for any health event that threatens the health of your lungs and eyes, the “wait and see” method doesn’t hold much water. As soon as you notice the signs of chlorine poisoning, it’s better to be safe than sorry by taking yourself or your kids straight to your nearest CareWell Urgent Care center.


A good recommendation is for parents on vacation to check the Ph and Chlorine Residual with a reliable Test kit like this sold on Amazon before using any Public Pool Water Facility or Indoor-Outdoor Water Park.

You have the right to know what your kids will be swimming in all day. So buy a test Strip or Testing Kit and carry it with you. Make sure you are testing the pool water chlorine with reliable reagents and equipment.


What is Combined Chlorine?

Combined Chlorine is the portion of chlorine in the water that has reacted and combined with ammonia, such as nitrogen-containing contaminants, and other organics that come from a swimmer’s perspiration, urine, and other waste. .……………………………………………………. Read more



JimGalloway Author/Editor



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