Pool Secret #10: Once a Bromine Pool . . . Always a Bromine Pool!

There are some neat pool products out there that can be really useful. Unfortunately, some of these products have "gotcha's" that your dealer often won't mention. [He may not know, himself!]

And, while a product's 'gotcha' may not get you, it's nice to know up front, or at least I think so.

Possibly one of the worst offenders in this regard is bromine. Many swimming pool owners tend to think of bromine as something they can try, and then abandon at will.

Not so! Here's why:

Br- + HOCl ==> HOBr + Cl-

Want that in English?

Here it is: chlorine converts 'used up' bromine (bromide) back to free bromine, and in the process, is converted itself to 'used up' chlorine.

As a result, as long as even 2 or 3 ppm of bromide ions remain in the water, you CAN'T have a chlorinated pool. And since bromine can't be stabilized, you also CAN'T have a stabilized pool.

So read the label before you pour: if it says anything about 'bromine' or 'sodium bromide', think twice. Do you really want a brominated pool? If you do, pour away!

But once you pour, if you change your mind there are two solutions.

You can drain it all.

Or, wait. Possibly for a long time. But just how long is uncertain.

Sunlight can convert sanitizing bromine compounds into permanently inactive bromates. Also, some chemists claim that a portion of the bromide oxidized by chlorine is converted to inactive bromates, instead of sanitizing bromine compounds. So on an outdoor pool, which gets lots of sun, and which is shocked with chlorine, a long time may only be a few weeks, instead of months.

Complicated Note:
Jock Hamilton, president of United Chemical sells a line of pool specialty chemicals that are based on sodium bromide. He claims that bromide in pool water breaks down rapidly, rather than slowly. Apparently, he's right . . . at least for outdoor pools exposed to sunlight.

Let me state it this way: in pools exposed to sunlight, bromine persistence is usually a long-term problem ONLY if the pool is brominated with any form of bromine tabs!

If bromine has NEVER been added to an outdoor pools in the form of tabs, shocking the pool (5+ppm of chlorine in a single dose), added on sunny days, will tend to remove the bromine/bromide. However, repeated doses may be needed.

On all indoor pools, and on all pools treated with bromine tabs, the only practical way to remove the bromine is to drain the pool.

The difference seems to be DMH ( dimethyl hydantoin ), a molecule used as a chemical 'coat-hook' for BioLab to hang the bromine and chlorine when creating the solid form of bromine, BCDMH (bromo-chloro-dimethyl hydantoin), sold in the USA. After the chlorine and bromine are gone, the DMH hangs around, affecting water chemistry in a variety of unpublicized and mostly undesirable ways. If DMH is present, it is VERY hard to get rid of the bromide without draining the pool.

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