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 Products | 5,000 Gallons | 10,000 Gallons | 15,000 Gallons | 20,000 Gallons | 25,000 Gallons | 30,000 Gallons |
---|---|---|---|---|---|---|
Bleach (8.35%) | 7.5 oz | 15 oz | 22.5 oz | 30 oz | 37.5 oz | 45 oz |
Cal-Hypo (48%) | 1.4 oz | 2.8 oz | 4.2 oz | 5.6 oz | 7.0 oz | 8.4 oz |
Chlorine Gas | 0.7 oz | 1.4 oz | 2.1 oz | 2.8 oz | 3.5 oz | 4.2 oz |
Dichlor | 1.2 oz | 2.4 oz | 3.6 oz | 4.8 oz | 6.0 oz | 7.2 oz |
Lithium-hypo | 1.9 oz | 3.8 oz | 5.7 oz | 7.6 oz | 9.5 oz | 11.4 oz |
Trichlor | 0.7 oz | 1.4 oz | 2.1 oz | 2.8 oz | 3.5 oz | 4.2 oz |
Chlorine Products | 5,000 Gallons | 10,000 Gallons | 15,000 Gallons | 20,000 Gallons | 25,000 Gallons | 30,000 Gallons |
---|---|---|---|---|---|---|
Bleach (8.35%) | 15 oz | 30 oz | 45 oz | 60 oz | 75 oz | 90 oz |
Cal-Hypo (48%) | 2.8 oz | 5.6 oz | 8.4 oz | 11.2 oz | 14 oz | 16.8 oz |
Chlorine Gas | 1.4 oz | 2.8 oz | 4.2 oz | 5.6 oz | 7 oz | 8.4 oz |
Dichlor | 2.4 oz | 4.8 oz | 7.2 oz | 9.6 oz | 12 oz | 14.4 oz |
Lithium-hypo | 3.8 oz | 7.6 oz | 11.4 oz | 15.2 oz | 19 oz | 22.8 oz |
Trichlor | 1.4 oz | 2.8 oz | 4.2 oz | 5.6 oz | 7 oz | 8.4 oz |
Chlorine Products | 5,000 Gallons | 10,000 Gallons | 15,000 Gallons | 20,000 Gallons | 25,000 Gallons | 30,000 Gallons |
---|---|---|---|---|---|---|
Bleach (8.35%) | 22.5 oz | 45 oz | 67.5 oz | 90 oz | 112.5 oz | 135 oz |
Cal-Hypo (48%) | 4.2 oz | 8.4 oz | 12.6 oz | 16.8 oz | 21 oz | 25.2 oz |
Chlorine Gas | 2.1 oz | 4.2 oz | 6.3 oz | 8.4 oz | 10.5 oz | 12.6 oz |
Dichlor | 3.6 oz | 7.2 oz | 10.8 | 14.4 oz | 18 oz | 21.6 oz |
Lithium-hypo | 5.7 oz | 11.4 oz | 17.1 | 22.8 oz | 28.5 oz | 34.2 oz |
Trichlor | 0.7 oz | 1.4 oz | 2.1 oz | 2.8 oz | 3.5 oz | 4.2 oz |
There are several chlorine products on the market, and there are a few notable differences between them.
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” Tablets | Stabilized | 90 | Decrease |
1” Tablets | Stabilized | 90 | Decrease |
Dichlor | Stabilized | 56 | Neutral |
Cal Hypochlorite | Unstabilized | 68 | Increase |
Liquid Chlorine | Unstabilized | 10 - 15 | Significant Increase |
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:
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.
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-
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.
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, 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.
Below are some tips on using chlorine to keep your pool clean.
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.
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.
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.
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.
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.
Pool chemicals should be added in the following order: alkalinity, pH levels, calcium hardness, stabilizer, and then chlorine.
You can use chlorine test kits to measure free chlorine and total chlorine.
Homeowners can measure their chlorine by using a chlorine test kit.
The ideal ratio of chlorine to water is 1 to 3 parts per million.
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.
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.
You’ll need to use a test kit to determine if your chlorine levels are 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.