Using sodium bromide along with chlorine

[chem geek]

You are correct that Mr. Ed was wrong in saying the bromide/bromine would be gone in 24 hours. I think we covered that in later posts between he and I. If you don't overdose with a lot of bromide, then one can expect over weeks and months that it will drop from bromine outgassing and from bromide/bromine water dilution.

The most common occurrence is not that bromine becomes bromamine but that the UV in sunlight breaks down bromine into bromide salt. Then any oxidizer, including chlorine, will reactivate it (oxidize it) back to bromine. That is mostly what happens. Only a small portion of the bromine reacts with bather waste to produce bromamines because the bather load in residential pools is fairly low. Also, you don't get stuck with bromamines because just like chloramines (at least inorganic ones so ones combined with ammonia) they get further oxidized and you end up again back with bromide salt.

If one wants a short-term high CYA workaround, then using an ammonium product to produce chloramine would be easier to get rid of when one was done. For sodium bromide, there is a complicated way to distinguish between bromine and chlorine. It involves the fact that the salicylate ammonia test kit actually measures monochloramine (it adds Dichlor in the test to convert ammonia to monochloramine) so if you take a water sample and add enough ammonia to it for 1:1 with chlorine or bromine, then you can use the ammonia test kit and if it measures something, then that amount (adjusting for unit differences) is chlorine and whatever was not measured in that test is bromine. To know the size of a bromide bank, you'd need to add enough chlorine to convert it all to bromine (i.e. add excess chlorine relative to bromide).

 

[Tepelus]

Bromine is easy to protect therefore it is not expensive to have a pool sanitized with bromine. Any pool cover will reduce the UVB and prevent bromine destruction. It is not a compex/difficut job to have a swimming pool sanitized with bromine: JUST ADD BLEACH. So, for a private person it is very simple.
Pool has to be covered when not in use
Add bleach in the evening
Make sure the pH is correct.

 

[chem geek]

Yes, a pool cover works wonders for chlorine as well. That's why I have only 1 ppm FC per day loss even though the pool is used every day. My mostly opaque electric safety cover reduces chlorine loss, virtually eliminates evaporation, and helps prevent heat loss though not as well as a bubble-type cover would.

 

[scott_home]

I know this thread is 2 years old. I had mustard algae in my pool around that time. I shocked the pool 2 or 3 times a year to control it but it kept coming back. About 4 months ago, I dumped all the salt water to convert back to non-SWG pool. A few weeks later, the mustard algae started to appear again. Very frustrating! This time I used Sodium Bromide before it got too serious. Look and behold, I have not had any major mustard algae outbreak ever since. One month ago, I forgot to put enough tabs in the skimmer and the algae started to show when I brushed. A preventive dosage was all it needed to get rid of it. I know some board experts may have a negative view on sodium bromide. But it works for me and my chlorine consumption is the same as before. Good luck to others who are fighting the mustard algae!

 

[Donldson]

I know this thread is 2 years old. I had mustard algae in my pool around that time. I shocked the pool 2 or 3 times a year to control it but it kept coming back. About 4 months ago, I dumped all the salt water to convert back to non-SWG pool. A few weeks later, the mustard algae started to appear again. Very frustrating! This time I used Sodium Bromide before it got too serious. Look and behold, I have not had any major mustard algae outbreak ever since. One month ago, I forgot to put enough tabs in the skimmer and the algae started to show when I brushed. A preventive dosage was all it needed to get rid of it. I know some board experts may have a negative view on sodium bromide. But it works for me and my chlorine consumption is the same as before. Good luck to others who are fighting the mustard algae!

Two years of algae problems, ripped out your SWG, dumped all your water, dumped in sodium bromide, and not a single thread asking for help during any of that?

Yeah, thanks for the advice. I'll pass. I would tell you why it is such a terrible idea, but clearly you got it all figured out.

 

[YippeeSkippy]

Please, Scot- if you ever go to sell your home, make sure to let the buyers know you've got a bromide pool.

I've been concerned lately about new pool owners struggling with pools they can't understand and have wondered if they are dealing with bromide without knowing.

Maddie

 

[scott_home]

Hi guys,

I am just telling others what works in my pool. I am not interested in the chemistry. I don't want to be like the guy earlier in this thread getting attacked by the "experts". I don't sell sodium bromide and have no interest in pool business. Your miles may vary. My pool has been very clear since I put sodium bromide. By the way, I only used it twice in 4 months. Initially half of a bottle. Then 1/8 of a bottle. I use about 4 chlorine tabs per week. My pool gets full sun from 11 am to one hour before sunset.

By the way, I stopped using the SWG not because of the algae. It is because salt water is corroding my limestone coping. I used stone sealer but salt water still won.

If you have not used this product, please let others know it in your comments. Hearsay evidence does not hold anything. Peace!

 

[Donldson]

I am not interested in the chemistry.

Then I humbly suggest you take your uneducated opinions elsewhere. We are interested in facts, not reviews by people who are proud that they don't know anything about pool chemistry. Go to Amazon if you want to offer your 5-star review of something you know nothing about.

Meanwhile I will continue helping the many people that have come to the site with terrible FC demand who have to drain their pools because of taking advice by people who have no idea what sodium bromide is but "it cleared my pool!" A real shame people aren't required to disclose how much they actually know about pool chemistry before offering their hearsay reviews of products online, isn't it?

Peace. If you have anything else to share please make sure it includes some form of data or chemistry. We don't deal in "it worked for me" here.

 

[pooldv]

Well, I do know a few things about pool water chemistry and all I have to say about sodium bromide is that I will NEVER put it in my pool or my hot tub.

 

[Zoey227]

Welcome to TFP! It would be great to have another person (in addition to those we already have) validating the chemistry as a cross-check as well as providing new insights.


This is not surprising because bromine is not moderated in its strength by Cyanuric Acid (CYA) so kills algae faster than chlorine with CYA. For green algae this isn't an advantage since chlorine alone at reasonable levels relative to CYA is enough to prevent algae growth (I suspect your FC was too low for your CYA level). For an SWG pool, an FC that is at least 5% of the CYA level should prevent green algae growth. Yellow/mustard algae is more resistant to sanitizers so would need up to double that level to keep it from growing, so usually we recommend eradication by shocking with high chlorine levels, getting behind light niches and under ladders, etc. Sodium bromide to produce bromine will also work, but has side effects I'll talk about below.


Your electrochemical reaction is neglecting to account for the usage/consumption of chlorine which is an acidic process. The net result with a steady-state that maintains an FC level is pH neutral. The rise in pH comes from a combination of carbon dioxide outgassing which is enhanced by the increased aeration from the hydrogen gas bubbles and is also caused by any undissolved chlorine gas that outgasses. See this post for technical details about the electrochemical reactions AND reactions of usage/consumption of chlorine. By understanding these principles, many SWG pool owners have been able to significantly reduce the rate of pH rise in their pools through methods such as keeping their Total Alkalinity (TA) lower, using sufficiently high CYA levels (usually close to 80 ppm) if the pool is exposed to sunlight, and using 50 ppm Borates for additional pH buffering and mild algae prevention/insurance.

Furthermore, the assumption that higher pH slows down chlorine production is incorrect. The production of chlorine in the SWG is the same at higher pH unless scale starts to form more significantly, which perhaps is what you meant. If you meant that at higher pH there is less of the active form of chlorine, hypochlorous acid, compared to hypochlorite ion, that effect is largely buffered by the presence of CYA as is shown by the graphs in this post.


Most of the thousands of SWG pool owners on this forum (and other related forums) are able to maintain their pools without getting to the green pool state because they maintain an FC sufficient for their CYA level. The industry recommendation of 1-3 ppm FC is simply too low with their 60-80 ppm CYA recommendation. Prevention is easier (the same is true for the non-SWG pools). When the CYA is high, the use of bromine (from sodium bromide) or the use of a non-chlorine shock (e.g. MPS) or other oxidizer will oxidize algae more quickly and one can also use clarifiers or flocculants, but all of these have side effects. For bromide, you then have a bromine pool, at least for a while. For MPS, it's quite expensive and you increase sulfates. Clarifiers and flocculants don't oxidize or kill so only supplement filtration/vacuuming.


Bromine outgasses. The Henry's Law constant for hypobromous acid is around 6100 M/atm while for hypochlorous acid it is around 930 M/atm. If there were no CYA in the water then bromine would outgas more slowly than chlorine, but because of CYA the chlorine outgas rate is quite slow (it's actually hypochlorous acid that outgasses in addition to molecular chlorine at pool pH; see this spreadsheet to see that the HOCl is about 420,000 times higher in concentration than Cl₂(aq) mostly making up for the lower Henry's Law constant for Cl₂ of 0.093 M/atm) and is much slower than the bromine outgas rate since the HOCl concentration is reduced by well over 50 by the CYA so the effective Henry's Law constant relative to FC is more like 46,500 M/atm. Using bromide instead of bromine tabs will have the outgassing go faster because the DMH in bromine tabs behaves somewhat like CYA to chlorine, though doesn't bind to bromine as strongly (though we've never gotten definitive equilibrium constants for that). If one has an ozonator, then ozone oxidizes bromide to bromine and oxidizes bromine to bromate, the latter being an end-point chemical (likewise, ozone also oxidizes chlorine to chlorate).


While the bromine is still in the pool it will tend to break down from sunlight more quickly because none of it is bound to CYA so you may notice a greater demand so need for a higher SWG on-time. Also, bromine smells differently as do bromamines compared to chloramines (say, on your skin when you get out of the water) so your pool may smell different (some don't like the bromine smell). The brominated trihalomethanes (THMs) are mutagenic and increase cancer risk (though it's a very low risk) while the chlorinated THM chloroform does not. Finally, the reason the bromine works is that it is at higher concentration because CYA is not moderating it. This means that it oxidizes swimsuits, skin and hair faster as well, similar to what chlorine does in pools without CYA (unless the FC is very, very low).

As for bromine effects on the SWG cell itself, I have no idea. I suspect it's OK, but don't know for sure. Coatings on SWG cells can be esoteric and therefore finicky.


The PAN Pesticides Database indicates that Suncoast Stop Yellow is nearly pure sodium bromide. So 4-8 ounces weight per 10,000 gallons would be 3-6 mg/L of sodium bromide for (3-6)*79.904/102.894/2 = 1.16-2.33 ppm Br₂. So this isn't that much so should outgas I would think within a month or so. For comparison, an FC that is at 5% of the CYA level has the same active chlorine level as 0.05 ppm FC with no CYA which is why I referred to the faster oxidation rate of bromine against swimsuits, skin and hair (notwithstanding some bromine vs. chlorine reaction rate differences and reaction selectivity differences).

One clever way you might be able to measure your bromine level separate from your chlorine level is to add a small amount of ammonia to your water sample to convert all bromine to monobromamine (NH₂Br) and all chlorine to monochloramine (NH₂Cl). Except for possible bleed-through from the monochloramine, it should not show up as Free Chlorine (FC) in the test, but monobromamine will show up as FC due to the monobromammonium ion (NH₃Br⁺) that may release a highly reactive positively charged bromine ion (Br⁺; see this paper for technical details) that reacts with DPD (and is back-titrated with FAS-DPD). If you have only chlorine, then it should all show up as CC (in the same amount that it would show up as FC if no ammonia were added and if there were no initial CC). Obviously, one needs to use a FAS-DPD test kit to have any reasonable accuracy and should use a 25 ml sample size so each drop represents 0.2 ppm.

Wow. You people are brilliant! Good job and wow you are super smart!!