Chlorine & Bromine Essentials

Chlorine is one of the most produced chemicals in the US. It has been said that without chlorine, 80% to 90% of the worlds population would not have safe clean water to drink.

When chlorine is added to water, it is turned into hypochlorous acid and hypochlorite ions. The hypochlorite ion does not actively contribute to the sanitizing ability of chlorine, but is an extremely effective oxidizer. The hypochlorous acid is the active, killing form of chlorine and what does the actual sanitizing. Chlorine kills bacteria, it does it very quickly. The Association of Analytical Chemists uses a kill time of 30 seconds to completely destroy a given concentration of bacteria as a standard for a hot tub, spa and swimming pool disinfectant.

The amount of hypochlorous acid and hypochlorite ions that are produced when chlorine is added to the water is directly related to the pH of the water. At a pH of 6.0, 96% of the chlorine will become the desired “killing” form of chlorine. At a pH of 7.0, 75% of the chlorine will become hypochlorous acid and at 8.0 the concentration is 25%. At a pH of 7.5 (the average spa) the amount of hypochlorous acid produced is about 50%.

The hypochlorous molecule will continue to “kill” until it combines with a nitrogen or ammonia compound to become a chloramine, or is broken down into its basic components. Chloramines have very little sanitizing ability and are the cause of many irritating problems, including eye and mucous membrane irritation and the source of harsh chlorine odors. “Free available chlorine” at levels up to 10-20 ppm has no detectable taste or odor and causes no irritation.

LIQUID CHLORINE/BLEACH: The advantages of liquid chlorine are that it is inexpensive upfront and it is easy to use. Liquid chlorine is unstable and is combined with sodium hydroxide to increase stability. There is about 12%-15% available chlorine and this amount can be further by heat and time. Typically, liquid chlorine will lose its effectiveness in as little as 30 days. Chlorine bleach is a weaker form at about 6% available chlorine which gives it a longer shelf life.

GRANULAR CHLORINE-SODIUM DICHLOR: A powder form of chlorine. Sodium dichlor is fast dissolving. Granular chlorine contains 56-63% available chlorine, Sodium dichlor also contains cyanuric acid, which prevents the reduction of chlorine loss due to the sun. Since granular chlorine has high available chlorine and is fast dissolving, it can be used for regular pool chlorination or for shocking a pool, all without adding any by-products to the pool water. Granular chlorine will not cloud the water upon initial application. Sodium dichlor also has pH value of 6.8, which is near the desired pH range (7.2 to 7.8). Finally, granular chlorine has a long shelf life. The real disadvantage of sodium dichlor is that it contains cyanuric acid which builds up quickly in the water and prohibits the chlorine from effectively sanitizing and oxidizing the water. Many states prohibit the use of chlorinated isocyanurates from being used in public spas.

GRANULAR CHLORINE-CALCIUM HYPOCHLORITE: Calcium hypochlorite is a quick dissolving powder made by passing chlorine gas over shale. The calcium shale is able to hold onto the chlorine molecule and release it when dissolved in water. This is a much better alternative to sodium dichlor but due to its calcium content, it will add to the water hardness and can leave a scale ring on the tub at the waterline and leave scale deposits on the heater element. Calcium becomes less soluble as temperatures increase.

CHLORINE TABLETS: Chlorine tablets come in two sizes: 1″ tabs and 3″ tabs. Chlorine tablets are purchased by pool and spa owners in the greatest volume because it is typically one of the cheapest forms of chlorine and is available in many places. Chlorine tablets contain 90% available chlorine, making it the strongest form you can buy except for gas. Chlorine tablets also contain cyanuric acid, which prevents the reduction of chlorine loss due to the sun but can make chlorine ineffective at higher levels. Chlorine tablets have a pH value of 2.8 to 3.0, which is very acidic, even more so then bromine tablets. Because it is so acidic, pH and alkalinity levels will drop and cause dissolving of metallic materials if not properly managed. This acidity is also a cause of metal staining.


BROMINE: A chemical in the halogen family that is an alternative to chlorine used for killing bacteria, living organisms, and other contaminates that are present in hot tub water.

TYPES OF BROMINE: Bromine is an alternative to chlorine. Bromine comes in both tablet and granular form. Bromine tablets are far more popular than granular bromine.

There are certain differences between bromine and chlorine. Bromine is more stable than chlorine at higher water temperatures. Which is why bromine is an overwhelming choice to sanitize spa water. Due to the presence of ammonia, bromamines (like chloramines) will be present in pool water. But, unlike chloramines, bromamines are somewhat effective at assisting with sanitizing the water and do not have the highly offensive odor that chloramines do.

The main drawback of bromine is that it is expensive. Combined with Potassium Peroxy Monopersulfate the expensive non-chlorine shock that typically accompanies bromine’s use-bromine is very expensive. Unlike chlorine, bromine cannot be protected from UV by cyanuric acid, but when used in a hot tub this is not really an issue. Even in spas using chlorine, it is not advised to use cyanuric acid due to it’s effects on the ability of chlorine to sanitized. In fact, some states prohibit the use of cyanuric acid in public spas.

The pH value of bromine Is 4.0, which like chlorine tablets is very acidic and will lower pH and total alkalinity which leads to corrosion. Therefore, like chlorine tablets they should not be placed in the skimmer. To manage this characteristic of bromine, check the pH often and place the bromine tablets in a bromine feeder.

BROMINE FUNCTION: Bromine itself is a sanitizer and disinfectant for water; it needs a catalyst such as chlorine or Potassium Peroxy Monopersulfate in order to oxidize water. Bromine tablets typically contain 60% bromine, 28% chlorine, and 12% as inert (other) ingredients including BCDMH which will render bromine ineffective as the concentration increases in the water. This is why it is necessary to drain and re-fill hot tubs in a relatively short amount of time. By oxidizing, bromine will kill all bacteria, living organisms, and other contaminates that are found in water. By oxidizing, bromine will kill all potential disease-carrying capabilities of these bacteria, living organisms, and other contaminates. But, bromine by itself has no ability to oxidize.

You cannot just add bromine and expect to have clean and clear spa water. The bromine level must be continually monitored as it will fluctuate based on bather and contaminant load these are factors that will lead to additional bacteria, living organisms, ammonia, and other contaminates being constantly present in your pool water. Regular shocking will help maintain clean and clear water. If you have a sodium bromide residual of at least 1,800 ppm or more, it is easy to make bromine by shocking with a non – chlorine shock, liquid bleach or calcium hypochlorite. Never use a shock using sodium dichlor.

Bromine will combine with, but cannot successfully oxidize, ammonia by itself. For this reason, you must shock your spa or hot tub on a regular basis.

“BROMAMINES”: Bromine must kill all bacteria, living organisms, , and other contaminants? Well, like chlorine, bromine is very effective at killing bacteria, living organisms, and other contaminates but when ammonia is present, bromine will combine with it, but cannot successfully oxidize it and the two combine to form “Bromamines.” Bromamines will remain in the water, and will register as bromine, but they are not as effective at sanitizing or oxidizing as “Free” bromine; unlike chloramines, bromamines are at least marginally effective at continuing to sanitize. Ammonia is commonly present in spa water from swimmer wastes (perspiration, urine, saliva and body oils), or even from some suntan lotions. No matter how ammonia enters a spa, it will exist.

Since bromamines are only marginally effective at sanitizing and oxidizing, they need to be removed from the water by shocking the spa on a consistent and regular basis. Even if you maintain a 2.5 – 4.0 ppm bromine reading at all times by just adding bromine tablets to the pool. The presence of ammonia will lead to Bromamines, preventing the bromine from being fully effective. The only to effectively oxidize Bromamines, is by shocking the water.

Over time, Bromamines will break down by themselves. But, since they are only marginally effect at sanitizing and oxidizing, bromamines should be eliminated from the water by shocking the spa regularly. Unlike chloramines, bromamines will neither irritate your eyes or skin, nor will they lead to an unpleasant odor.

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