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    All About Pool Chlorine and Alternatives

    Pool Chlorine and Bromine - America's Most Popular Pool Water Sanitizer

    Proper pool water sanitization is absolutely necessary for the maintenance of a clean and healthy swimming pool. While there are a variety of different pool sanitizers available for pool owners to use, the two most commonly used sanitizing chemicals are chlorine and bromine. While both of these pool chemicals provide excellent pool sanitization, it's important to understand the differences between the two options before deciding which sanitizer to use in your swimming pool.

    When chlorine or bromine is added to pool water, a reaction takes place which results in the product of the chemical's active disinfectant form. The active disinfectant form of chlorine is Hypochlorous acid (HOCL), while the active form of bromine is Hypobromous acid (HOBr). The reason why these chemicals are used as swimming pool sanitizers is because they are able to effectively and inexpensively kill bacteria and other contaminants which can cause dirty, cloudy pool water and can also pose as a risk to swimmer health.

    How Chlorine & Bromine Work to Sanitize Pool Water

    Hypochlorous acid (chlorine's active form) kills bacteria and other pathogens by attacking the cell walls and internal structure of microorganisms. This process is known as oxidation and renders the microorganisms harmless. As the active chlorine molecules combine with bacteria and other microorganisms, those chlorine molecules become inactive. Over time, chlorine molecules in the pool water will also combine with ammonia and nitrogen, resulting in the formation of chloramines. Since chloramines and inactive chlorine molecules do not assist in the water sanitization process, regular addition of chlorine to a swimming pool is necessary in order to maintain clean water.

    Pool shock is a necessary product, to remove chloramines as they build up in the water. Otherwise, accumulating chloramines can produce a strong, unpleasant odor & can also cause skin and eye irritation. Another important fact to remember is that chlorine is very pH-dependent. This means that the effectiveness of chlorine is dictated by the pool water's pH level, which must be maintained between 7.4 and 7.6 in order for proper chlorine sanitization to take place.

    Bromine in its active form (Hypobromous acid) kills and deactivates pathogens in the same general way that chlorine does. Also similar to chlorine, bromine combines with nitrogen and ammonia to form bromamines. However, unlike chloramines which are very poor sanitizers, bromamines are very effective sanitizers. This means that bromine does not need to be added to swimming pools as frequently as chlorine. While occasional pool shocking will be required to prevent water turbidity caused by the build-up of bromamines, this step will not be required as frequently as with chlorine. Another difference between chlorine and bromine is the fact that bromine is effective over a wider pH range. In fact, bromine will effectively kill contaminants when the pH level is anywhere between 7.0 and 8.0.

    Bather Experience

    When swimming pool chlorine is maintained at the correct levels, its odor is practically undetectable and it generally will not cause any irritation. However, improper pool maintenance and improper pool shocking can lead to the accumulation of chloramines. As already mentioned, chloramines do have a strong and unpleasant smell and can cause significant skin and eye irritation. Also, some swimmers are allergic or sensitive to chlorine and therefore must swim in pools which use an alternative sanitizer such as bromine. In contrast to chloramines, bromamines have a far less pungent odor and do not cause skin and eye irritation.

    Ease of Use

    When it comes to using these swimming pool chemicals, many pool owners find chlorine generally easier to use. Which chlorine type is best for you? Chlorine is available in a variety of forms, such as 3” tablets, 1” tablets, sticks and granules (which can be added manually to pool water as it dissolves very quickly). Chlorine levels are quite easy to control when the water is shocked regularly, and when pH and alkalinity levels are maintained within ideal ranges. Cyanuric acid (also known as "Stabilizer") should also be added to chlorine pools as needed, to maintain the level between 30ppm - 50ppm. Stabilizer helps reduce the breakdown of chlorine due to sunlight.

    Bromine use, on the other hand, can be slightly more complicated. To begin with, bromine is a very slow dissolving chemical and must be added to pool water through the use of an automatic chemical feeder. Because the use of a chlorine product may be necessary to maintain the free bromine level, pool owners may have questions or need advice when first starting to use bromine as a pool sanitizer. Bromine breaks down quickly in sun light so more bromine will need to be used in outdoor pools than will be needed for indoor pools. Bromine is more effective than chlorine in hot temperatures, which is why bromine is most commonly used in spas and hot tubs.

    Chlorine & Bromine – FAQs:

    When Was Chlorine First Used?

    What we know as "Chlorine" was first discovered in the 16th century, and today it is used in a variety of industrial products, as well as many household products we need & use every day. In fact, chlorine is one of the most produced chemicals in the US!

    What Exactly is Chlorine?

    Chlorine is a by-product of the electrolysis of salt water. When electricity is passed through salt & water (2NaCI & 2H20) the atoms dissociate into (chlorine, sodium Hydroxide & Hydrogen (CI2 + 2NaOH + H2). The CI1 is isolated in a gaseous state, and is used to create other chlorine compounds used for sanitizing, bleaching and in the production of plastics and related industrial products.

    How Does Chlorine Sanitize Pool Water?

    When chlorine is added to water, it causes a reaction which produces HOCI (hypochlorous acid) + HCI (hydrochloric acid). Hypochlorous acid is the active (bacteria-killing) form of chlorine, which sanitizes water. Chlorine kills microorganisms by breaking through the cell walls and destroying the inner enzymes, which in turn deactivates, or oxidizes the cells. The hypochlorous molecule continues this process until it either combines with nitrogen or ammonia compounds to become a chloramine, or it is broken down into its component forms, becoming de-activated itself.

    Is Chlorine Dangerous or Unhealthy?

    If not handled properly, chlorine can certainly be a caustic & dangerous chemical to work with, with some forms being more dangerous for the user and the environment than others. At levels found in swimming pool or spa water, chlorine poses no danger to swimmers or pets. Allergic reactions to chlorine are rare. However, some people may experience skin irritation. Additionally, chloramines (common in poorly balanced pool & spa water) are typically the cause of occasional red eyes when swimming. Extremely high levels of chlorine in the water could possibly release gases under certain conditions that can cause breathing difficulties.

    The main hazard in working with chlorine is to the person adding the chlorine to the pool or spa. Care should always be taken, and manufacturer's label instructions always followed. When opening a container of chlorine, always be aware that breathing in excessive chlorine vapors can cause unconsciousness and can even be fatal. You should always wear protective gloves & goggles when handling chlorine. If your skin comes in contact with chlorine, wash it off with plenty of warm water to prevent irritation. If chlorine splashes into your eye, irrigate the eye with water and contact a physician immediately. Most importantly, never mix chlorine with ANY other chemical (not even a different type of chlorine!) as this can cause a great toxic gas or even a powerful explosion! Dirt, debris and foreign substances such as algaecides, alkalis, acids, etc. can cause spontaneous combustion when mixed with chlorine.

    Pools have little to no impact on the outside environment. As a closed system, your pool or spa doesn't contact nature very much. There could be some potential hazard involved with waste water from a pool that has either extremely high chlorine levels or extremely low pH levels. But it is unlikely that the amount of water expelled during backwashing your filter could pose much harm. Pool water is similar in make-up to the water that flows out of your tap. many people who water their lawns are exposing the environment to higher chlorine and lower pH than is found in their pool water! While there are certain industrial uses of chlorine that are potentially harmful, in a swimming pool environment the potential hazards are much lower, even nonexistent. There has been much publicity and controversy over the use of chlorine in recent years. Some organizations have even called for bans on its use. Our recommendation? You decide if chlorine is right for you, your pool, your situation. For more information on chlorides, contact the Association of Pool and Spa Professionals.

    What Different Types of Chlorine Are There?

    In its elemental state, chlorine exists in a gaseous form. This type of chlorine is available for swimming pool sanitization; is very cheap, and is the purest form of chlorine, with no binders or carriers. This type of chlorine features 100% available chlorine. It is also extremely dangerous and is therefore restricted in its use. It is rare to find a pool that uses chlorine gas as a sanitizer, and those that do are usually older, very large public pools that have enacted strict safety procedures. Gas is also very acidic, with a pH close to muriatic acid, so pools that do it must also add a lot of base to counteract the acidity.

    Liquid chlorine is created by bubbling the chlorine gas through a solution of caustic soda. This yellow liquid is stronger, extremely corrosive & chemically identical to bleach. It has 10-15% available chlorine, and a pH on the other end of the scale (at 13). Liquid Chlorine is called Sodium Hypochlorite (NaOCI) and because it is already in solution, sodium hypo produces Hypochlorous acid instantly when it contacts water. The liquid can be poured directly into the pool. The use of liquid chlorine is more common in larger commercial pools which have it delivered in large vats. For most residential pools, its lower cost seems to be outweighed by difficulty in use, as well as the amount of acid that is required to counteract its pH of 13.

    Tri-chlor is a solid form of chlorine available in stick or tablet form. "Tri-chlor" is short for Trichloro-s-triazinetrione (a stabilized form of chlorine that has become very common in residential pools in recent years). "Stabilized" means that it contains cyanuric acid pressed into the tablet itself. It features 90% available chlorine & a somewhat low pH level at 3, so the pH in your pool may gravitate downward. This form of chlorine is slow-dissolving, so it works well in floaters or in-line erosion feeders. Using tablets in the skimmer is not recommended because of the corrosive nature of the chemical that would come in contact with metal pipes and equipment. This becomes more of an issue if your filter pump operates on a timer, as Tri-chlor can strip out the internal copper components of a pool heater. It remains however, an effective & inexpensive method of controlling algae. Tablets should also not be thrown directly into the pool, as they can stain and etch plaster & bleach, as well as deteriorate your vinyl liner.

    Another form is granular Di-chlor, (short for Sodium Dichloro-s-triazinetrione). Di-chlor is made in the same manner as Tri-chlor, but the two products are very different. The pH of Di-chlor is a very acceptable 7, and it dissolves rapidly and goes right to work on contaminants. Di-chlor has less chlorine (only 62% available chlorine). Because it contains cyanuric acid, it lasts longer than other unstabilized forms of granular chlorine. It can be used as a shock treatment oxidizer, or for normal everyday sanitation. Di-chlor's main drawback is cost, as it is perhaps the most expensive form of chlorine available.

    Calcium Hypochlorite is commonly available in its granular form, but can also be purchased in tablet form. "Cal-Hypo" is a commonly used shock treatment throughout the country. Although not stabilized with cyanuric acid, it has a quick kill rate against algae and chloramines, and features 65% available chlorine and a high pH level of nearly 12. It does not dissolve as rapidly as more powder-like forms of granules, so it's a good idea to pre-dissolve cal-hypo into a bucket of water before broadcasting it into a pool. Its popularity is due mainly to availability and low price. Cal hypo is more dangerous and unstable than other forms in that it is very dusty and becomes contaminated easily by foreign substances which can cause combustion. Mix only with water, don't breathe the dust, and always keep the lid tightly secured & clean.

    How Much Chlorine Should I Add?

    Each pool has its own chlorine demand, and we can't tell you how many tablets or how many pounds or gallons you'll need for your particular pool. A good starting place is a quality water testing kit. Factors such as size, water capacity (in gallons), amount & frequency of use, water balance and pH can all have an effect on how much chlorine you'll need to use. With a little experimentation, you'll be able to determine how much chlorine it takes to achieve a consistent minimum level of 1.0 ppm (parts per million). As an example, first test the water, then add three tablets to your feeder. Check the residual again in 12-24 hours. If it's too low, add more, if it's too high, remove some. Fairly soon you will develop an idea of your pool's particular chlorine demand. Remember also that demand can change during the warmer months, among other things. As chlorine is an expansive and corrosive compound, make every attempt to avoid consistently over-chlorinating the pool, as this can irritate swimmers skin & eyes. If you have questions or need advice, feel free to contact our Pool Experts at 1-800-983-7665.

    What Impact Does pH Have on Chlorine?

    The power of chlorine is greatly influenced by how well you manage your water's pH level. As the pH of your pool water increases, the killing power of your chlorine decreases. At a pH of 6.0, you will achieve approximately 96% of the potential from each pound of chlorine. But at what cost? Such a low pH would also wreak havoc on all surfaces the water comes in contact with (for example your equipment, pool surface, liner, and the swimmers themselves). It's just too corrosive. By pushing the pH up to 7.0, the efficacy of the chlorine drops to 73%. Raise it up to 8.0 (where many a pool seem to drift to), and it drops dramatically... down to 21%! At a perfect pH level of 7.5, we can expect to have about 50% of our chlorine in the molecular structure of Hypochlorous acid (the active, killing form). The remaining half is in the form of hypochlorite ion, which is also an active form of chlorine, but very weak and slow to kill.

    What is Meant by "Total", "Combined" and "Free" Chlorine?

    These are states of existence for the chlorine molecule. If a molecule is "free", it has not bonded with another compound, and is therefore available for sanitizing. When free chlorine molecules encounter and destroy a nitrogen or ammonia-containing compound, they combine with them to create a "combined" chlorine compound (also called chloramines). The chloramine is no longer available to sanitize anything, and it blocks the path of free chlorine molecules, and creates a strong odor associated with chlorine. Combined chlorine level can be tested with a test kit that measures total & free levels separately, and allows the tester to determine combined levels by subtracting the two valves. "Total" chlorine is simply the sum of combined and free levels.

    What is meant by "Shocking" (or "Super-Chlorinating") Pool Water?

    These terms are synonymous for oxidizing the pool water. By raising chlorine levels ten times the level of chloramines, a threshold is reached called "breakpoint chlorination". When this occurs, something of a shock rips through the water, killing everything in its path.

    When should you shock your pool water?

    Some recommend shocking the pool when combined chlorine levels reach 0.3 ppm. Others recommend it once every few weeks, whether it needs it or not. Use your sense to determine the need for shocking. If the pool water is cloudy or hazy because somebody left the filter off or forgot to add chlorine, your eyes may tell you it's time to shock. If you notice a strong chlorine odor in the water and notice eye irritation during swimming, you may sense the need for shocking. Large doses of chlorine are also very effective when algae have turned the water or pool walls a yellow or green color.

    How much chlorine is required to effectively shock?

    Generally, you want to raise the chlorine level up to around 10 ppm. When using cal hypo, you'll find at least one bag per 10,000 gallons will be sufficient. A little more wouldn't hurt, because if you don't reach the crucial level of breakpoint chlorination, not only is the chloramine problem not solved, but matters have been made potentially worse. Always follow instructions on the package of granular chlorine or non-chlorine shock (which may be potassium peroxymonosulfate). Liquid chlorine can also be used for super-chlorination. Whatever chemical you choose, the goal is to introduce 10 times the level of the chloramines. For example, if combined chlorine levels are at 1.0 ppm, we need 10 ppm of free chlorine levels to reach breakpoint.

    What is Meant by "Stabilizer"?

    Cyanuric acid is a chlorine stabilizer, which is designed to provide a chemical cloak around the chlorine molecule to protect it from the sun's UV radiation (the largest killer of your chlorine). Stabilizer can be a real money-saver during the hottest times of the year. A test kit can measure how much Cyanuric acid is present in the water. Recommended levels from the National Spa & Pool Institute are at 30-50 ppm. Stabilizer(also called "Conditioner") is fed directly into the skimmer at a rate of 4 lbs. per 10,000 gallons of water. It dissolves inside the filter and you will immediately see a reduction in chlorine demand. If you are using chlorine from the iso-cyanurate family, the Cyanuric acid is already present in the tablet and you shouldn't need to add any additional, unless the level is below 30-50 ppm.

    While Chlorine & Bromine can take a little time to understand, you'll soon find that they are both reliable, effective and relatively easy-to-use pool water sanitizers. If you have any questions about these two pool chemicals, how to use them (or what alternatives might be available), feel free to call our friendly Pool Experts at 1-800-983-7665.

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