Water Parameters for Bromine:
Bromine is primarily used in spas but can be used in swimming pools also. The increased cost of operating a pool on bromine makes chlorine a more efficient decision. Expert Pool & Spa recommends the use of Dichlor Granular Chlorine for use in pools and spas. Unlike bromine, dichlor is more pH stable and less expensive to use. Bromine tends to cause a brown staining on the spa surfaces and fittings and is difficult to remove. Bromine is a more complicated system than chlorine and proper knowledge is essential for bromine to work properly.
Bromine, like chlorine, is a chemical element of the halogen family and is a prominent pool or spa disinfecting agent. Bromine compounds used for pool or spa disinfection are manufactured in granular, liquid, and tablet form. Elemental bromine is a liquid, and is rarely used today to disinfect pools or spas.
The advantages of bromine include a more stable level of disinfecting power at higher water temperatures, and less objectionable smell. However, the cost of bromine can be double or triple that of chlorine. Bromine consumption can be cut down by building up a residual bank of 8 ppm of hypobromous acid. This can be done by starting the system with liquid or powder sodium bromine.
Chemistry of Bromine:
The chemistry of bromine and chlorine is similar in many respects. Bromine compounds dissolve in water forming hypobromous acid, an effective disinfectant. The acid changes, especially at high pH, to the hypobromite ion. Likewise, in the presence of nitrogen compounds like urine, bromamines form. But the differences in the effect of the compounds formed are significant.
Hypobromous acid is the main disinfecting and oxidizing form of bromine. At higher pH levels, hypobromous acid dissociates into hypobromite ions and hydrogen ions. The hypobromite ion is also an active disinfectant. In addition, hypobromous acid does not dissociate to the same degree as chlorines hypochlorous acid when pH increases. This means that bromine remains more active than chlorine when pH increases.
Bromamines (combined bromine) are formed when hypobromous acid destroys nitrogen-bearing organic matter. Bromamines are active disinfecting agents (unlike chloramines). They don't irritate swimmers' eyes or cause objectionable odors. In these respects they are more desirable in pool/spa water than chloramines.
Bromine is commonly available in two forms, a one-step treatment system or a two-step system. Each type can be fed automatically through special feeding equipment called brominators.
Some experts advise that a previously untreated pool or spa be started with sodium bromide to build up a residual bank (up to 8 ppm of hypobromous acid). This reserve bank cuts down on bromine consumption later.
A common form of bromine used to treat pool/spa water is organic hydantoin bromine.
This one-step bromine system uses bromo-chloro-dimethyl-hydantoin (BCDMH), an organic compound of bromine and chlorine available in tablet form. As the tablet dissolves in water, it releases chlorine and bromide ions which react forming hypobromous acid - the disinfecting agent.
The organic bromines like BCDMH have a pH around 4.0. Monitor pH, total alkalinity and adjust when needed. Total alkalinity in the range of 100-120 ppm is advisable when using hydantoin bromine.
Organic bromine tablets can be used in chemical feeders or floaters.
Be aware that bromine dissolves much faster above a temperature of 90º F. This can be a source of trouble in spas at 104º F. Be sure to use only a spa bromine feeder to avoid overbromination.
The two-step bromine disinfectant system uses sodium bromide (a bromine salt in powder form) and a separate oxidizer - monopotassium persulfate.
Bromide salts are contained in sea or ocean salt. Bromide salt is added to the water sodium bromide (granular or liquid), where it dissociates into sodium and bromide ions. Then the oxidizer or "activator" is added, turning the bromide ions into hypobromous acid - the active disinfectant. The oxidizer is commonly monopotassium persulfate or potassium peroxymonosulfate. Sometimes chlorine is used.
The oxidizer/activator works to reactivate combined bromine as well.
Be aware that 2-step bromine systems have a low pH (4 to 6). The pool/spa pH should be tested and adjusted on a regular basis.
Testing Bromine Residual:
Since all three forms of bromine - hypobromous acid, hypobromite ions, and bromamines - are active disinfectants, the Total Bromine Residual reading is an accurate measure of the amount of active disinfectant. There is no need to measure the total and combined levels to determine the free bromine level, as for chlorine. The bromine residual should be maintained between 2.0 and 4.0 ppm.
Test water with bromine test strips, DPD or OTO test kits calibrated for bromine. If not calibrated, the bromine residual equals the chlorine residual reading times 2.25.
Shocking has two goals: regenerating the active bromine, and oxidizing excess organic materials in the water.
Though bromine is an aggressive disinfectant, compared to chlorine it is not a good oxidizer. Therefore shocking on a regular basis to eliminate algae and organic contaminants is essential in bromine-treated water. It is particularly important in spas, to eliminate bather contaminants like oils and lotions. Depending on conditions (dull water, some algae growth, higher amount of organic materials in the water), you may need to shock bromine-treated spas as often as daily, and pools twice a month.
Shocking of bromine-treated water can be done with a chlorine product or a non-chlorine product. The non-chlorine oxidizer/activator potassium monopersulfate can be used for shock treatment. Chlorine-bearing chemicals used for shock treatment include lithium hypochlorite, calcium hypochlorite, and sodium hypochlorite. The chlorine itself is used up during shocking, so no residual remains.
If you wish to switch from bromine to a chlorine disinfectant and stabilizer for an outdoor pool or spa, the bromine concentration already in the water will interfere with cyanuric acid's ability to inhibit chlorine degradation by UV light.
To switch from bromine to stabilized chlorine treatment, pools must be partially or fully drained and refilled until they contain under 0.2 ppm of bromine.
~ Expert Pool & Spa, Inc. ~