Last Updated: June 29, 2022

Pool Chlorine Calculator

Written By: Pool Care Guide

Chlorine is the disinfectant that is most frequently used in swimming pools. 

The amount of Chlorine in a pool is determined by three main measurements; Combined Chlorine (CC), Free Chlorine (FC), and Total Chlorine (TC). In most cases, the Free Chlorine test is carried out since it represents the amount of Free Chlorine in water available for disinfecting. 

Residential pool chlorine levels should be kept between 1 - 3 PPM. You’ll likely find the chlorine dose you need by using the chlorine calculator below or one of the three chlorine PPM Charts.

Chlorine Dose Tables

Doses to Raise Chlorine PPM by 1

Chlorine Products5,000 Gallons10,000 Gallons15,000 Gallons20,000 Gallons25,000 Gallons30,000 Gallons
Bleach (8.35%)7.5 oz15 oz22.5 oz30 oz37.5 oz45 oz
Cal-Hypo (48%)1.4 oz2.8 oz4.2 oz5.6 oz7.0 oz8.4 oz
Chlorine Gas0.7 oz1.4 oz2.1 oz2.8 oz3.5 oz4.2 oz
Dichlor1.2 oz2.4 oz3.6 oz4.8 oz6.0 oz7.2 oz
Lithium-hypo1.9 oz3.8 oz5.7 oz7.6 oz9.5 oz11.4 oz
Trichlor0.7 oz1.4 oz2.1 oz2.8 oz3.5 oz4.2 oz

Doses to Raise Chlorine PPM by 2

Chlorine Products5,000 Gallons10,000 Gallons15,000 Gallons20,000 Gallons25,000 Gallons30,000 Gallons
Bleach (8.35%)15 oz30 oz45 oz60 oz75 oz90 oz
Cal-Hypo (48%)2.8 oz5.6 oz8.4 oz11.2 oz14 oz16.8 oz
Chlorine Gas1.4 oz2.8 oz4.2 oz5.6 oz7 oz8.4 oz
Dichlor2.4 oz4.8 oz7.2 oz9.6 oz12 oz14.4 oz
Lithium-hypo3.8 oz7.6 oz11.4 oz15.2 oz19 oz22.8 oz
Trichlor1.4 oz2.8 oz4.2 oz5.6 oz7 oz8.4 oz

Doses to Raise Chlorine PPM by 3

Chlorine Products5,000 Gallons10,000 Gallons15,000 Gallons20,000 Gallons25,000 Gallons30,000 Gallons
Bleach (8.35%)22.5 oz45 oz67.5 oz90 oz112.5 oz135 oz
Cal-Hypo (48%)4.2 oz8.4 oz12.6 oz16.8 oz21 oz25.2 oz
Chlorine Gas2.1 oz4.2 oz6.3 oz8.4 oz10.5 oz12.6 oz
Dichlor3.6 oz7.2 oz10.814.4 oz18 oz21.6 oz
Lithium-hypo5.7 oz11.4 oz17.122.8 oz28.5 oz34.2 oz
Trichlor0.7 oz1.4 oz2.1 oz2.8 oz3.5 oz4.2 oz

Chlorine Products

There are several chlorine products on the market, and there are a few notable differences between them.

  • Stabilized - Chlorine evaporates quickly in direct sunlight. Stabilizers help keep the chlorine in the pool, but they do make the chlorine less effective.
  • Free Chlorine - Free chlorine is chlorine that is ready to sterilize the pool of bacteria.
  • pH - pH is how we describe the level of acidity. If we lower the pH, that means we raised the acidity. If the acidity is lowered, it increases the availability of chlorine. With more chlorine available, the pool is cleaned even better. That said, don’t lower the pH below recommendations (7.2 to 7.4) or you’ll hurt your pool.

The Different Types of Chlorine for the Pool

What is the chlorine type?Is it stabilized?What is the percentage of free chlorine in this product?What effect does it have on the pH?
3” TabletsStabilized90Decrease
1” TabletsStabilized90Decrease
DichlorStabilized56Neutral
Cal HypochloriteUnstabilized68Increase
Liquid ChlorineUnstabilized10 - 15Significant Increase

What Will Happen if the Chlorine Dose Is Too High?

The cure is in the dose. If the dose is too little, biological contaminants will overtake your pool. If swimmers are exposed to high chlorine levels, they might experience the following symptoms: 

  • Burning sensation in the eyes, nose, skin, and throat, 
  • Coughing and wheezing
  • Nausea and vomiting
  • Shortness of breath
  • Watery eyes
  • Dizziness
  • Rashes

More About Pool Chlorine

Chlorine is a popular disinfectant because it effectively eliminates most bacteria, algae, and disease-causing microorganisms present in the water. However, some parasites such as Giardia and Cryptosporidium are chlorine resistant. If you decide to remove those organisms, you’ll need to use ozone or UV.

Pool chlorine is consistently consumed by contaminants such as sweat, dirt, urine, or feces droplets from swimmers’ bodies. Water also evaporates in the presence of heat or direct sunlight, and the newly formed mist or water droplets free up chlorine. It is also vital to note that water pH directly affects chlorine concentration. 

That is why it is essential to test pool chlorine levels every other day, even in pools with a chlorine generator. Ensure that the free chlorine levels in the pool do not reach zero. If this happens, the pool water will be susceptible to contamination from microorganisms and other forms of contaminants. 

Hypochlorous Acid

Commonly referred to as free chlorine, hypochlorous acid (HOCl) is the active agent that oxidizes the inorganic and organic materials present in chlorinated water. It is formed when chlorine dissolves in the water. 

The formula for the chemical reaction is as follows:

FC=HOCl + OCl-

Effects of Low Free Chlorine < 1 PPM

If the chlorine levels in the pool fall below 1 PPM, there is nothing to protect it from contaminants. Microorganisms and parasites are therefore likely to build up. The pool is likely to turn green or cloudy and create an unsafe swimming environment. A cloudy pool also means that drains are not visible, and swimming in such an area can be dangerous. 

Effects of High Free Chlorine > 4 PPM

A 1-3 PPM free chlorine level is recommended for residential pools, while commercial pools should have 3-5 PPM. Free chlorine levels of over 10 PPM are required to shock the pool. The negative effects of high free chlorine depend significantly on the cyanuric acid (Stabilizer or CYA)levels available in the water. 

Swimmers are likely to experience discomfort if the pool has an unbalanced pH or contains high levels of combined chlorine (CC). If a pool has a free chlorine level of PPM or above, swimmers should put off all activity until the chlorine level drops. They can either use a chlorine neutralizer to speed up the process or wait for the free chlorine levels to fall naturally. 

Combined Chlorine (CC)

Combined chlorine, which is also referred to as chloramines, is one of the main causes of irritation and discomfort to swimmers in a chlorinated pool. It is also responsible for the bleachy smell that often comes from chlorine pools. 

A pool with a very strong bleach smell is likely to contain high levels of combined chlorine, and swimmers are more likely to experience irritated skin, red itchy eyes, and irritated mucous membranes. 

Tips on Pool Chlorine

Below are some tips on using chlorine to keep your pool clean. 

Using Store Bleach for Pool Chlorine

The liquid bleach you purchase in stores is chlorine. It is, therefore, applicable in raising the chlorine levels in your pool. However, it is essential to note that bleach can come in different concentrations. Store bleach with additives and scented bleach should not be added to pools. 

Effect of pH on Chlorine

The effectiveness of chlorine can change drastically depending on the pH levels of your pool water. For instance, chlorine is only 3% effective at 8.0 while 97% effective in water with 6.0pH. Ideally, swimming pool water should have a pH of between 7.2 and 7.4 to allow for chlorine effectiveness of approximately 50%. We don’t want it higher than that because the free chlorine will be used up too quickly.

On the chart below, you will notice how the pH affects HOCL (Hypochlorous Acid) and OCl- (Hypochlorite Ion). Both of these are considered free chlorine, but hypochlorous acid is 80 to 100 times more effective at killing microorganisms. If we can bring the HOCL to 50%, we will find the best balance between cleansing power and longevity.

How Much Chlorine Is Needed to Shock the Pool?

In order to reduce the combined chlorine levels in a pool, shocking the swimming pool water is necessary to achieve the chlorine breaking point. 

A simple way to achieve this is by increasing the chlorine PPM by ten times the total combined chlorine. To ensure that the shocking process achieved the breaking point, check that the free chlorine and total chlorine levels are equal. Both levels should also rise at the same time if more chlorine is added to the water. 

How Long Should You Wait to Use the Pool After Adding Chlorine?

A pool is considered safe for use if the chlorine level is below 5 PPM. You can use the pool roughly 4 hours after adding Chlorine, as long as this level isn't exceeded. In most public pools, swimming is allowed 2-4 hours after adding Chlorine. You can use a test strip or chemical reagents to test the chlorine levels in your private pool. 

What Are the Benefits of Using Chlorine in Pools?

Chlorine plays a huge role in keeping pool water clean. It reduces the likelihood of illness if the water enters swimmers' bodies through accidental swallowing or mucous membranes. Saltwater pools also need Chlorine. In most cases, they generate it automatically. 

While there are several other pool cleaning methods such as ozone and UV, they shouldn't serve as replacements for Chlorine. 

Such methods are beneficial in cleaning water before it enters the pool, while Chlorine maintains the hygiene of the water inside the pool. Moreover, swimmers are continually introducing new contaminants to pool water, and Chlorine can fight them effectively. 

In the absence of Chlorine, the harmful microorganisms and bacteria found in pool water have the potential to cause illness and infections. Harmful microbes present in contaminated water can cause skin, eye, ear, gastrointestinal, neurologic, wound, and respiratory infections. CDC reports that swimmers commonly suffer from diarrhea after swimming in contaminated pools. 

It is, however, essential to note that Chlorine doesn't act on bacteria instantaneously. Therefore, swimmers must maintain basic hygiene, such as taking a shower before entering the pool and rinsing off all shampoos, soaps, and conditioners. Avoid relieving yourself inside the pool, and do not go swimming if you have diarrhea. 

Safety Practices

  • Chlorine and pH test kits should be used frequently to maintain safe and effective levels
  • Store chlorine in an environmentally controlled location that is between 50°F - 70°F (10°C - 21°C) dry, shaded, and protected from the weather
  • Wear appropriate protective equipment such as gloves, goggles, and clothing.
  • Follow the instructions listed on the chlorine product.
  • Implement adequate ventilation

Questions and Answers

What Chemicals Should I Balance First in My Pool?

Pool chemicals should be added in the following order: alkalinity, pH levels, calcium hardness, stabilizer, and then chlorine.

How Do You Calculate Free Chlorine and Total Chlorine?

You can use chlorine test kits to measure free chlorine and total chlorine.

How Do You Measure Chlorine in the Water?

Homeowners can measure their chlorine by using a chlorine test kit.

How Much Chlorine Should Be in a Pool?

The ideal ratio of chlorine to water is 1 to 3 parts per million.

Can You Put Too Much Chlorine in a Pool?

Too much chlorine will make the pool temporarily unsafe for swimming, but it will make it cleaner. Fortunately, any chlorine that isn’t stabilized will quickly evaporate. That’s why you can typically swim in a pool the day after a pool shock that massively spikes chlorine levels.

How Often Should I Put Chlorine in My Pool?

Chlorine levels should be tested 2 to 3 times per week, and chlorine should be added if levels fall below the recommended minimum of 1 PPM.

How Do I Know if I Have Too Much Chlorine in my Water?

You’ll need to use a test kit to determine if your chlorine levels are too high.

What Happens if Your Chlorine Is too High?

High chlorine levels aren’t a problem as long as nobody goes swimming at that time. The high chlorine will make the pool a bit cleaner before evaporating back to safe levels over the next 24 hours. Make sure to test those levels before taking a swim.

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