Chlorine and Bromine: A Comparison

periodic-table-lgChlorine and Bromine sit one atop the other in the periodic table, nestled between Flourine and Iodine, two other halogen sanitizers.

Although related, chlorine and bromine are actually very dissimilar, and respond to aqueous environments in completely different ways.

Molecular Activity

Chlorine, in it’s elemental gaseous form, is the most active and reactive halogen. Liquid and dry forms of chlorine also provide more rapid disinfection, when compared to bromine tablets.

But stabilization with pool conditioner, aka cyanuric acid, retards the active “hunt and kill” behavior of free chlorine, making your chlorine sluggish and tired.

Bromine tablets, those that use the BCDMH recipe, are protected from the sun in a different manner, and the activity of bromine in a pool is roughly the same as stabilized chlorine. Our bromine tablets are a mixture of 61% bromine, and 27% chlorine, but require no stabilization.

taylor-dpd-cl-brHowever, it is generally accepted that when using bromine, one should increase the residual by a factor of two, or double the dose. This may lead you to think that you would use double the amount of bromine tablets.

Initially – yes, until a bromine bank builds. After a few weeks, bromides are reactivated by chlorine, boosting the residual, and bromamines (combined bromine – see below) can be counted as active sanitizers.

And chlorine it seems, should be double dosed as well! It’s worth noting that other chemists like myself – on sites like Pool Forum and TFP have stated that higher levels of cyanuric acid used in a chlorinated pool demands a higher level of free chlorine, for complete sanitation.

Molecular Stabilization

To stabilize a molecule means to protect it from it’s surrounding environment, and reduce the deleterious effects of light, temperature, pH or contaminants.

Chlorine stabilizer, or cyanuric acid, quickly combines with chlorine to protect the new compounds from absorbing ultraviolet light, which destroys chlorine molecules.

Bromine by contrast can be stabilized from ultraviolet light in a┬ábromo-chloro-dimethyI-hydantoin [BCDMH] form, by reducing it’s activity, and blocking absorption of degrading UV rays.

sluggish-chlorineStabilizing pH and alkalinity levels is another way to protect molecules in an aqueous solution, such as your pool, which should be maintained in the 7.4-7.6 range. Chlorine molecules become sluggish in a high pH environment, whereas bromine adapts readily to high pH levels. At a pH level of 8.0, 85% of bromine remains active, while chlorine musters only 25% of the troops.

Likewise, Cyanuric acid (CYA) slows down the Activity (kill rate and speed) of chlorine, and much higher free chlorine levels are recommended – for the best bacteria and algae prevention.

prescription“For a stabilized pool with cyanuric acid levels of 20-40 ppm, free chlorine levels should be maintained in the range of 3-5 ppm, for complete sanitation, and protection against bacteria and algae.”

This is why I also recommend swimming pools maintain lower cyanuric acid levels – between 20-40 ppm, for a happy medium between Activity and Stabilization. Test for CYA every 3-4 months, and if it rises above 50 ppm, drain a portion of the pool and refill.

Molecular Combinations

As bromine and chlorine evolve through their lifespan and encounter many contaminants, they morph into various forms. When ammonia or nitrogenous compounds are engaged, chlorine and bromine readily convert to chloramines and bromamines, respectively.

bromine-molecule-atomsBromamines formed in a pH range of below 9.0 still continue to behave as active sanitizers, whereas combined chlorine molecules become feeble sanitizers in a pool environment, losing their ability to destroy bacteria or algae.

chlorine-molecule-atoms-Chlorinated pools require more shocking than a bromine treated pool, to remove chloramines, when levels become noticeable (through smell or eye irritation) or when tests a DPD test shows combined chlorine levels to be present.

Bromine pools have little concern with building levels of bromamines, which are still active sanitizers with little smell or irritating effects. Shocking with chlorine will also lower combined bromine levels, and reactivate bromides in the water to boost your free bromine level.

Bromine has one more difference from chlorine – the price. Try as we do to bring the two prices closer to each other, bromine tablets continue to cost twice as much to produce, due to raw materials and energy costs.

Bromine tablets do have some quantifiable benefits that may justify paying more. Bromine is more stable at varying pH and temperatures. Combined bromine is still an active sanitizer, and bromides in our BCDMH tablets will regenerate to build residual and lower cost.

chlorine-is-king-2But chlorine tablets will always be king, at least until we figure out how to squeeze the market to reduce prices for the raw materials necessary to produce less expensive bromine!

Back to the lab!


Dr. Pool

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