Daily pool water disinfection 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. Both of these chemicals provide excellent daily pool sanitation, but it's important to understand the differences between the two options before deciding which pool sanitizer to use in your swimming pool.
Difference between Chlorine and Bromine
Bromine has certain advantages over chlorine, foremost being that users find the odor less objectionable, with fewer complaints of dry hair and skin. Although bromine tablets sanitize in the same way as chlorine tablets, bromine is more stable across a wider pH range, and unlike chloramines, combined bromine (bromamines) are still active sanitizers.
However, bromine cannot be protected from the sun, and burns off quickly in sunny outdoor pools. Secondly, bromine tablets are nearly twice the cost of chlorine tablets, due to the cost of raw bromine. However, after a short time of using bromine tablets, bromide ions can be regenerated by shocking the pool, which can lower tablet consumption and expense.
Most outdoor swimming pools use stabilized 3-inch chlorine tablets for daily sanitation. Indoor pools, small covered pools and hot tubs are more suited for using 1-inch bromine tablets.
How Chlorine & Bromine Work in Pools
When chlorine or bromine is added to pool water, a reaction takes place which results in the production of the chemical's active disinfectant form. For chlorine, the active disinfectant form is hypochlorous acid (HOCL) while the active form of bromine is hypobromous acid (HOBr). These active pool sanitizers are able to kill bacteria and other pathogens that pose a risk to swimmer health and also destroy algae, dirt and contaminants which can cause poor water quality and stained surfaces.
Hypochlorous acid, chlorine's active form, kills bacteria and other pathogens by attacking the cell walls and internal structures of microorganisms. 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, and other particles they cannot kill, resulting in the formation of chloramines. Chloramines are inactive chlorine and do not assist in the water sanitization process.
As such, pool shock is necessary to remove chloramines as they build up in the water and produce a strong, unpleasant odor, and also cause skin and eye irritation. When testing with a DPD test kit, you can calculate the amount of Total and Free chlorine levels, with the difference between the two being the Combined Chlorine or chloramine level.
Bromine in its active form, hypobromous acid, kills and deactivates pathogens in the same way that chlorine does. Also similar to chlorine, bromine can combine with nitrogen and ammonia to form bromamines. However, unlike chloramines which are very poor sanitizers, bromamines are very effective sanitizers, and they don’t smell or irritate eyes like chloramines.
Chlorine pool shock is still often used in bromine pools however (although you can use non-chlorine shock if you prefer) to reactivate bromide ions into free bromine molecules, and for removal of any bacteria or algae that may have escaped regular daily bromine treatment.
Bromamines and Chloramines
Imagine a free chlorine molecule, just released from the chlorinator, it travels through the pipe and is quickly shot out into the pool, where it floats around and encounters all types of microscopic particles. Being highly unstable, free chlorine is drawn towards most any particle in the pool, and destroys most instantly. Some other molecules however, such as nitrogen and ammonia, attach themselves to the chlorine molecule with chemical bonds, which reduces the free chlorine molecule to a very weak sanitizer, and a smelly irritant.
When Chloramine levels reach 0.3 ppm or higher, a chlorine pool should be super chlorinated to a level of 10 to 20 times the level of combined chlorine. For instance, for a Chloramine level of 0.5 ppm, add enough granular pool shock to raise the chlorine level up to 5 to 10 ppm. For best results, lower the pool pH to 7.2 before adding pool shock, to increase its activity and power.
Adding such a large amount of chlorine so quickly breaks the molecular bonds of combined chlorine molecules, while oxidizing the pool water to remove all organic and pathogenic particles. Adding less than enough shock however, won’t reach the critical threshold of breakpoint chlorination, so be sure to test and dose properly when shocking to remove chloramines.
When pool water has a near zero level of combined chlorine, or chloramine molecules, its odor is practically undetectable and generally will not cause any irritation. However, lax pool water testing, 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 skin and eye irritation. In contrast to chloramines, bromamines have a far less pungent odor and less skin or eye irritation. They also remain potent as a sanitizer, whereas chloramines lose all potency.
In addition, bromamines do not gas-off the pool surface, but stay in the pool, unlike chloramines, which tend to rise to the surface and release into the air. Chloramines corrode steel surfaces of indoor pool environments and cannot be good for those who breathe chloramine laden air, which tends to be strongest near the surface of the water.
Very high levels of bromamines may become undesirable and noticeable. Shock treatment of a bromine pool on a regular basis, to reactivate bromides and oxidize any stray contaminants, will also remove bromamines, to keep levels manageable.
Testing for Bromamines and Chloramines
Many test kits and strips do not test for both Free and Total chlorine, so you can’t determine the level of combined chlorine (formula is TC-FC=CC, or Total minus Free equals Combined). Any difference between Free and Total, or if the test sample darkens at all with the addition of the third DPD reagent, is a measurement of combined chlorine, or combined bromine.
DPD test kits will always test for free chlorine, but only those with 3 chlorine reagents test for total chlorine as well. There are some pool test strips that test for both, and one called ShockChek that specifically checks for (only) free and combined chlorine, turning the pad pink when it’s time to shock the pool for chloramines. The most accurate way of testing for combined chlorine molecules is with an FAS-DPD test kit, or with a ColorQ Photometer.
Types of Pool Chlorine
Trichloro-S-Triazinetrione, or Trichlor for short, is what 95% of pool owners use to sanitize the pool on a daily basis. Most pool owners use the 3 inch tablets, although the larger chlorine sticks dissolve more slowly. Small 1 inch tablets are used for very small pools, or for very large pools; the smaller tablet size dissolves at a faster rate.
Calcium Hypochlorite, or Cal Hypo for short, is another type of chlorine that can be used for daily sanitation in pools and fountains. CCH chlorinating tablets, which must be used in a CCH feeder, offers a calcium based tablet that is not stabilized, and does not add cyanuric acid to the pool. Cal Hypo is also available as a type of granular pool shock treatment, which is unstabilized and not economical for use as a daily sanitizer.
Sodium Dichloro-S-Triazinetrione, or Dichlor for short, is a stabilized form of granular chlorine that does not contain calcium, but is stabilized for protection from the sun. Dichlor is often used for fountains or small pools, hand-fed every few days, or used as a chlorine boost for larger pools during sunny hot weather. Dichlor can be used for daily chlorination or periodic shock treatment.
Sodium Hypochlorite, or Liquid Bleach for short, can be used in swimming pools to chlorinate on a daily basis or for shock treatment. Large commercial pools use bleach for both purposes, using small chemical pumps to inject the chlorine directly into return line injection fittings. Liquid chlorine contributes no calcium or cyanuric acid to the pool, but has a very high pH level.
As mentioned above, Trichlor tablets or sticks are the most common type of chlorine used. That’s true primarily because of the price and availability, but also because it’s one of the easiest and safest ways to disperse chlorine into the pool; just add the tablets to a feeder or floater to maintain a constant chlorine level in the pool.
Also as mentioned above, bromine tablets may be the best sanitizer choice for indoor pools, covered pools or spas and hot tubs. They aren’t suitable for outdoor pools exposed to the sun, only because it cannot be stabilized. Bromine tablets must be used in a Brominator only and should never be used in feeders that have been used for Trichlor tablets.
Granular chlorine products dissolve too fast, creating peaks and valleys in daily chlorine levels, but slow dissolve tablets deliver an even, consistent chlorine level.
Most residential pools use tablets for daily chlorination and granular pool shock for periodic shock treatment to remove bacteria, algae or chloramines. As an alternative to pool chlorine tablets, you can install a saltwater chlorinator, but will still need granular chlorine for the same reasons listed above, in addition to maintaining balanced water, so important for proper sanitation of pool water.