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A s you may already know, chlorine is the most popular swimming pool sanitizer, but there are a host of other sanitation methods currently in the industry that you can also use to keep your swimming pool clean. We will discuss in this article different types of pool chlorine and explain why it is so popular and effective for sanitizing your swimming pool water. Six (6) different types of chlorine, or chlorine compounds, are used in the sanitation of swimming pool water. Sanitizers come in liquid, powder, and tablet form, and many pool owners often have questions about the differences between them. These sanitizers are sodium hypochlorite, calcium hypochlorite, lithium hypochlorite, chlorine gas, and stabilized compounds trichlor and dichlor. In this article, we hope to get some of the questions you may have answered and learn more about these different forms of chlorine.
The World Health Organization has published international guidelines for the safety of swimming pools and similar recreational-water environments, including standards for minimizing microbial and chemical hazards. The United States Centers for Disease Control and Prevention also provides information on pool sanitation and water related illnesses for health professionals and the public. The main organizations providing certifications for pool and spa operators and technicians are the National Swimming Pool Foundation and Association of Pool & Spa Professionals. The certifications are accepted by many state and local health departments.
Chlorine is added to the 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.
If using cyanuric acid, a chlorine stabilizer, or chlorine products with cyanuric acid (for example, products commonly known as dichlor or trichlor [see product label]), CDC recommends pH 7.2–7.8 and a free available chlorine concentration of at least 2 ppm in pools. CDC recommends not using cyanuric acid or chlorine products with cyanuric acid in hot tubs/spas.
* Free available chlorine is the more active form of chlorine that kills germs.
Chlorine is readily available, affordable, and cost-effective, but the right swimming pool chlorine sanitizer for you will depend on your individual needs. Selecting the right chlorine sanitizer for your swimming pool is as much about personal preference as it is about several other factors such as cost, benefits, storage and even the location where you live. And there are those salt water chlorinators that turn salt into chlorine using a specialized generator. Sounds pretty awesome, right? As a swimming pool owner all you would have to do to turn salt into chlorine is just pour the required amount of salt into your swimming pool (unless you have a brine-tank system) and let the generator do the work. We will discuss salt chlorine generation more later.
Chlorine gas is the most potent form of chlorine product as it is 100% chlorine. It may be used by pool maintenance professionals as well as public pool complexes to raise free chlorine levels very efficiently, compared to chlorine acid liquid solutions. While chlorine gas was commonly used by professionals due to its efficiency in terms of both time and cost, it is probably overkill for most residential needs. It is an excellent disinfectant and has a relatively low price. But the cost of maintaining equipment, rising insurance premiums, training requirements, transportation, and high toxicity levels has significantly reduced its use over the years. Therefore, for safety reasons, gas chlorine has been banned in many places. Chlorine gas may also be dangerous and lead to poisoning if not handled correctly.
Sodium Hypochlorite, commonly referred to as liquid bleach, or just “bleach” by service technicians, is a liquid sanitizer that is both very common among pool professionals and cost effective. A household chemical widely used since the 18th century as a disinfectant or a bleaching agent, indeed the oldest and still most important chlorine-based bleach. It is made of a 12.5% sodium hypochlorite solution, but in fact, it is the least expensive form of chlorine sanitizer. Pool professionals like liquid chlorine because it may be added in bulk, which makes it a great solution for larger commercial pools.
There are some drawbacks to using bleach on private residential pools, however. One drawback is that liquid bleach has a pH value of 13 or higher. So, you will need to counter the pH effects of liquid bleach by adding muriatic acid to balance its impact. This reduces the overall cost benefit of liquid bleach. Another drawback is that liquid bleach can be highly corrosive to pool surfaces. If used improperly, the long-term costs of using liquid bleach can far outweigh the short-term savings. This form of chlorine also will increase the water’s total dissolved solids (TDS) due to its sodium chloride content (salt), but it has no negative impact on disinfection.
Sodium hypochlorite is not stable and eventually could lose strength over a period of time. It’s recommended that the product be kept in a cool, dark place. Even though we all use it regularly in our homes, we need to be careful when it comes to storage. Its corrosive properties, common availability, and reaction products make it a significant safety risk. In particular, mixing liquid bleach with other cleaning products, such as acids or ammonia, may produce toxic fumes. Always remember to wear protective clothing when handling chemicals. Sodium hypochlorite is a liquid, so it is recommended to have a secondary containment. This may make it very bulky and problematic with space requirements if you have limited storage area.
Byproducts in pool water: hypochlorous acid (HOCl) + sodium (Na+) + hydroxide (OH-)
Available chlorine by volume: 10-12%
pH: 13.0 (extremely alkaline)
Calcium Hypochlorite is the most popular powder sanitizer among private pool owners. Generally the commercial substances are sold with a purity of 65% to 73% chlorine concentration, mixed with other chemicals present, such as calcium chloride and calcium carbonate, resulting from the manufacturing process. As you can see having a relatively high concentration of chlorine, other than liquid bleach, it tends to be the most cost effective of chlorine sanitizers.
The primary things to be aware of are that cal-hypo will raise calcium hardness levels of your water. If water pool water stays too hard for too long, it can cause corrosion to the pool surface. Cal-hypo also has a high pH of about 12. So, acid will need to be added to maintain goal pH levels after adding cal-hypo. Cal Hypo comes in the form of powder or tabs; tabs require a feeder to be introduced to the water. These feeders tend to get clogged with calcium and organic waste buildup, sometimes referred to as “chalking”. The bigger issue with cal hypo, however, is its volatility. It is a very strong oxidizer and fire hazard, and when it is near certain chemicals (other types of chlorine, for example), it can spontaneously combust.
Byproducts in pool water: hypochlorous acid (HOCl) + calcium (Ca+) + hydroxide (OH-)
Available chlorine by volume: 65-75%
pH: 11.8 – 12.0 (strongly alkaline)
Dichlor is perhaps the most “best of all worlds” chlorine sanitizer. It is typically found in concentrations of 60-65%, which is comparable to cal-hypo. It is a powder sanitizer, which makes it easier to spread or broadcast around the pool than chlorine tablets. It is stable, which means it can be used as both a chlorine sanitizer and as a shock. Unlike Lithium Trichlor (below), this type slightly reduces the pH and total alkalinity of your pool water. It has a pH of 7, which means only a modest amount of pH increaser may be required with use of dichlor.
One drawback of dichlor is that, like trichlor, it raises cyanuric acid levels. This may be a problem if cyanuric acid levels get to high and you must replace some of your water. Another drawback is dichlor tends to be quite a bit more expensive that cal-hypo. Dichlor is a fire hazard, and is not easily introduced via an automated feeder system due to its fast-dissolving nature. This compound comes in two forms: anhydrous, which has a higher level of available chlorine and therefore is more hazardous for storing (Class 3 oxidizer), and dehydrate, which has a lower level of available chlorine. This merits a lower NFPA hazard classification (Class 1 oxidizer).
Byproducts in pool water: sodium cyanurate (NaH2C3N3O3) + hypochlorous acid (2HOCl)
Available chlorine by volume: 56-62% (but roughly 50-60% of that is cyanuric acid)
pH: 6.8-7.0 (neutral)
Chlorine tablets are an extremely common form of chlorine sanitizer for private and residential pools. They are cost effective in terms of both time and money because they are relatively inexpensive and can be dispersed passively. It is popular for year-round residential pools by putting tabs in the skimmer or floater.
The active ingredient, trichloro-s-triazinetrione (trichlor), is up to 90% chlorine which makes this form of sanitation highly efficient. Trichlor has a low pH, typically around 3, so pH increaser may need to be added to maintain pH balance between 7.2 and 7.8. The most important consideration when using these chlorine tablets is to ensure they disperse as evenly as possible. It is ill-advised to simply toss them into your pool. Instead, it is recommended using an automatic chlorinator. However, a simple chlorine dispenser is a suitable, more cost-effective option. Trichlor is volatile, and explosive when met with cal hypo. Trichlor is also very acidic, which can corrode metal components within the pool system, especially if the pump is not circulating water 24/7. Metals can dissolve when met with stagnant water with highly acidic trichlor. Eventually that metal content will fall out of solution and stain. Given what we know about the LSI, trichlor should never be used in cold months, as its pH almost guarantees etching and corrosion when the water gets cold.
Byproducts in pool water: cyanuric acid (H3C3N3O3) + hypochlorous acid (3HOCl)
Available chlorine by volume: 90% (but 55% of that is cyanuric acid)
pH: 2.8-3.0 (very acidic)
Lithium hypochlorite is quite a bit more expensive than other sanitizers due to the high demand of lithium in other industries, particularly batteries. This comes in granular form and its high cost make it a poor choice for many service companies, especially those charged with maintaining commercial pools. At 30-35% chlorine concentration, it is quite a bit weaker than some of the other solutions. However, it does have one primary benefit that has earned it a loyal following of one segment of pool owners. Lithium-hypo dissolves very quickly, which reduces the risk of bleaching effects in vinyl pools.
Byproducts in pool water: hypochlorous acid (HOCl) + lithium (Li+) + hydroxide (OH-)
Available chlorine by volume: 28-35%
pH: 10.8 (alkaline)
Tomas Leclerc is the owner of the consulting firm Aquatic Safety International, LLC. He is an educator, mentor, manager, and water safety advocate. Mr. Leclerc is passionate about teaching individuals how to be safe in & around the water, & contributing to prevent drownings. He is an experienced, motivated, driven, visionary, goal oriented, & dedicated aquatic safety educator & a risk assessment professional with thousands of hours invested at many aquatic facilities working for America’s leading insurance companies helping facilities be safer.
Mr. Leclerc is a published author, & researcher, with several publications in the area of aquatics, & was privileged to served for 4 years as an editorial review advisory board member with the International Journal of Aquatic Research & Education. He has conducted research in lifeguard training programs, water safety & have presented at several national conferences.
Specialties: Managing, Drowning Prevention, Water Safety Training, Staff Training, Aquatic Health, Safety, & Risk Management Assessments, Education Technology, Blended Learning, Marketing, Web Design, Swimming, Triathlons, Water Polo.
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This is very good information! To be safe takes knowledge, direction , information, training and so much more! Safety is a way of living! Knowing how to swim is just the beginning of been safe around water. It is so good to have a magazine that encompasses different aspects and point of views! ~ Frances Cabrera
Water Safety Magazine focuses on drowning prevention, and being safe in and around water. The mission is to educate, inform, have fun, and save lives.
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