Activating Bromide consumes Chlorine?

Whale

Member
Jan 29, 2019
11
Australia
Hello all, I've recently converted our saltwater in-ground pool (pebble surfaces) from chlorine to bromine.
After experiencing some water quality problems with algal growth, I added sufficient sodium hypocrite to raise the total chlorine to 5ppm.
That should have activated some of the stored bromide to produce around 2ppm of bromine, which it seems to have done, but now the total chlorine test shows virtually zero (?).
Is it correct to assume that the activation of bromide to bromine has consumed all of the sodium hypocrite (chlorine) that was added just 24 hours earlier?
If so, what concentration of bromine should be maintained, and would the output from a Saltmate Chlorinator over 8 hours normally be sufficient to activate that concentration?
Many thanks.
 

Bama Rambler

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I don't know much about Bromine, but I do know that some SWCG manufacturers warn against using their SWCG's in a Bromine pool. Did you check with Saltmate about using their unit in a Bromine pool?
 

Whale

Member
Jan 29, 2019
11
Australia
Thanks Dave, and no I didn't check the compatibility of the Saltmate unit, but now will. Still looking for responses re the main issue in my post, so feel free to move it to another Forum if necessary.
 

Whale

Member
Jan 29, 2019
11
Australia
Dave, I just checked with Saltmate, and there's no compatibility issues with their products in bromine sanitised pools provided salt is still present at required concentrations.
 

Whale

Member
Jan 29, 2019
11
Australia
Threads Merged
After adding bromine to my saltwater inground pool (65,000L) 3 months ago, I've had several bad experiences, and so have decided to move back to chlorine as a sanitisation agent WITHOUT DRAINING / REFILLING THE POOL.
My plan to add chlorine via my Saltmate Chlorinator, and to possibly suplement whatever chlorine is generated in that way with sodium hypocrite in liquid form to achieve around 5ppm of free chlorine at a pH of around 7.5.
That should activate sufficient bromide to produce around 2ppm of bromine and thus keep the pool properly sanitised.
My plan will take some time to exhaust the "bank" of bromide in the pool, and while rainwater ingress will require pumping to waste which will accelerate the depleation of bromide, does anyone have a better / quicker way to complete the conversion to chlorine? Is there a way to flocculate the bromide for removal by vacuuming to waste?
Many than in advance.
 

Bama Rambler

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That's good news. From now on you'll need to test for Bromine instead of chlorine in your pool. Just adjust your SWCG based on your Bromine reading like you would on the FC reading.
 

duraleigh

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I know nothing about bromine pools but remember this exerpt from one of Ben Powell's articles more than 10 years ago

"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! There are two solutions....

1. You can drain it all.
2. 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."
 

JamesW

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Mar 2, 2011
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suplement whatever chlorine is generated in that way with sodium hypocrite in liquid form to achieve around 5ppm of free chlorine at a pH of around 7.5.
That should activate sufficient bromide to produce around 2ppm of bromine and thus keep the pool properly sanitised.
5 ppm chlorine is 11.25 ppm bromine. Try to keep the chlorine at 2 to 4 to keep the bromine at 4.5 to 9.

One problem with bromine is that you don't have a stabilizer like you would with chlorine and cyanuric acid.

As long as you keep the chlorine at about 2 (bromine at 4.5), you should be fine.

Do periodic overnight chlorine loss tests to make sure that you're not getting behind on sanitation.
 

Whale

Member
Jan 29, 2019
11
Australia
Many thanks everyone, and YES you're right James, I got the chlorine:bromine ratio the wrong way around.
Right now a total chlorine reading of 2ppm in the early evening and with chlorinator / pump / filter then running for 8 hours is totally consumed by the oxidization process by next morning.
My plan was to supplement the chlorinator's contribution by adding hypochlorite to keep the chlorine higher than for a normally chlorinated pool in order to oxidize more bromide, and in that way get it out of my pool a bit sooner.
Not really "shocking" the pool as Duraleigh suggested, but is that a useful strategy, and if "shocking" is necessary, how often and how much hypochlorite in a 65,000L pool?
 

JamesW

TFP Expert
Mar 2, 2011
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I would suggest that you maintain the chlorine reading at about 2 to 4 and do a periodic OCLT to make sure that the sanitation and oxidation is sufficient.

Maintain the CYA at 60 ppm. It won't help with the bromine, but it can help identify when the bromide is being depleted and chlorine is beginning to be maintained.

Once you begin to maintain some chlorine, you should notice an increase in the chlorine levels without an increase in the amount of chlorine being introduced.

How much sodium bromide did you add?
 
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Whale

Member
Jan 29, 2019
11
Australia
Don't know, as a contractor who sells a "better chemical regime" added chemicals while I was absent. I've since found out that his cocktail involves sodium bromide, together with magnesium, boric acid, and zinc.
Right now, in the middle of a 40 deg day, the pool water is crystal clear and tests at hardness 200ppm, total chlorine 0.5, free chlorine not detected, pH 8, total alkalinity 180ppm, CYA not detected, ORP 770.
 
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JamesW

TFP Expert
Mar 2, 2011
14,999
Ok, I would follow my earlier recommendations for chlorine and CYA.

I would get the CSI to between -0.3 and 0.0.

I would get the TA down to about 60 and then keep the pH at about 7.8.
 

Whale

Member
Jan 29, 2019
11
Australia
I'm back.........

The chlorine that I'm adding to my pool is still being consumed by the oxidisation of bromide to bromine; 4ppm in the early evening is down to <1ppm by morning.

I can live with that for the time being, but as I'm concurrently trying to keep the pH at around 7.8, I added some hydrochloric acid this morning and it immediately turned the pool water in the area yellow.

It quickly dissipated, but why did that happen, and will adding CYA as JamesW suggested have the same effect?

PS....There's magnesium in the water as added by the pool guy (see post #11)
 

JamesW

TFP Expert
Mar 2, 2011
14,999
When you add acid to a bromine pool, the acid can turn the hypobromous acid into elemental bromine, which will be yellow.

"Expert" needs help. LOL

The bromide gets oxidized by the chlorine into bromine but you don't lose anything.

1 mole of chlorine creates 1 mole of bromine. So, the test will come out the same.

If you're losing a lot of bromine overnight, then you have something in the water that requires a SLAM.

You should expect to see a lot of loss during the day because bromine is not protected by cyanuric acid.
 

Whale

Member
Jan 29, 2019
11
Australia
Thanks James,
You may remember from my previous posts that I'm trying to convert my bromine pool back to chlorine, and I understand that until all the bromide is "lost" that added chlorine will be consumed.

My question relates to your suggested addition of iso-cyanuric acid, where even though I understand your rationale, will that also result in elemental bromine being formed, AND create issues?
 

JamesW

TFP Expert
Mar 2, 2011
14,999
The bromide isn't going anywhere anytime soon. I suspect that they added a lot of sodium bromide based on the acid turning the water yellow.

Unless you drain and refill, you're going to have a bromine pool for probably up to a year or more.

The cyanuric acid won't cause a problem.

How long are you running the pump per day?

How much are you running the SWG per day?

What are all of your chemistry readings?
 

Whale

Member
Jan 29, 2019
11
Australia
With the chlorinator isolated due to manual addition of 3L hypochlorite, after running the pump/filter for 8 hours overnight the pool chemistry was total hardness 200ppm (calcium equiv), total chlorine 4ppm and total bromine therefore around 9ppm, free chlorine 3ppm, pH 8.5 (before adding acid), total alkalinity 120, cyanuric nil.
 

JamesW

TFP Expert
Mar 2, 2011
14,999
Ok, at this point, I would use the SWG to maintain the chlorine at about 2 to 4.

Without a drain and refill, you're just going to have to live with a bromine pool.

I would recommend a periodic OCLT to make sure that the oxidation and sanitization are adequate.

If you fail the OCLT, then you need a SLAM.

I would add about 40 ppm cyanuric acid.

Once you get the SWG dialed in to where the chlorine never goes below 2 and you always pass the OCLT, you should be good.

If the bromide gets low enough, you should see that the normal chlorine level begins to stay higher without adding more chlorine than normal.
 

Whale

Member
Jan 29, 2019
11
Australia
Many thanks once more James. I'll do as you suggest, and not so patiently wait for all the bromide to be used-up.

With the benefit of hindsight I should never have allowed the pool guy to convert our pool to his "special" chemical regime......that's substantially bromine.