Turn High CYA Pool into a Bromine Pool?

[poolnoob.ca]

Today there was a thread asking about using iodine as a sanitizer, which made me search other similar threads. I found one in which chemgeek mentioned that bromine is not bound to CYA like chlorine is. That got me to thinking: for pools with unmanageable high CYA that can't be drained, for example currently in California due to the drought, would it be feasible to turn the pool into a bromine pool for sanitation, as it is not affected by CYA? Then once it is possible to drain and refill go back to standard chlorine?

 

[JamesW]

I think that it's worth considering. Add sodium bromide and oxidize it with liquid chlorine or a swg.

 

[JoyfulNoise]

Wouldn't the high CYA reduce the effectiveness of chlorine at oxidizing the bromide to bromine? Would that then necessitate more expensive MPS shock?


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[JamesW]

No, the available hypochlorous acid would oxidize the bromide. As the chlorine becomes chloride, more chlorine would be released and oxidize more bromide.

I would think that there would be very little chlorine left because almost all would be used up oxidizing bromide into bromine.

Overall, it's not an ideal solution, because the bromine has very little protection from the sun. It is difficult to maintain an adequate bromine level. The best solution would be to use an SWG for more continuous bromine creation.

 

[JoyfulNoise]

I had read somewhere (not on TFP) that you can not use an SWG with bromide present as the electrolysis of chloride to chlorine also produces bromates (BrO3^-) which do not sanitize and are considered carcinogens by the EPA.

Do you know if this is correct?


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[chem geek]

This is the basis for many United Chemical products based on sodium bromide. While it works around high CYA, it turns the pool into a bromine pool and you can only get back to chlorine with significant drain/refill unless you carefully limit the amount of sodium bromide that is used. Generally the oxidizer demand in such bromine pools is higher because while bromine breaks down more slowly than chlorine (with no CYA), bromine is not bound to CYA so the net result is that it generally breaks down faster than chlorine with CYA -- roughly 50% to 100% faster. One can try and compensate for this by maintaining a relatively low level, but that may be harder to do.

You can use an SWG with bromide and it produces bromine and there are some systems such as the Frog system used in spas that do just that. I think you are mixing up ozone which reacts with chlorine to produce chloride and chlorate and reacts with bromine to produce bromide and bromate and also reacts with bromide to produce bromine. So with ozone and bromine the net result is that it produces some bromine from bromide but also converts some bromine to bromate and stops there. So over time bromide is depleted and bromate builds up. While bromate is an EPA-regulated drinking water contaminant due to being a carcinogen, it is not absorbed by the skin so in a pool or spa isn't a big concern since you aren't drinking large quantities of pool or spa water.

 

[JamesW]

Note that the SWG would be used to create chlorine and the chlorine would create the bromine from bromide.

The bromide levels would be kept fairly low so there would only be a small fraction of bromine created directly by the cell.

I have seen people use SWGs to maintain a bromine pool and it does work.

 

[chem geek]

Yes, but with an SWG there's really no point in turning a chlorine pool into a bromine pool. This thread is about having a pool with very high CYA turn into a bromine pool. Presumably a pool with an SWG shouldn't have a very high CYA since one shouldn't be adding Trichlor or Dichlor to it. Now if for some reason someone did inappropriately get their CYA too high in an SWG pool, then I agree with you that it would work to turn it into a bromine pool.

It would be good to develop/use a test that could validate the size of the bromide bank or otherwise distinguish between chlorine and bromine so that one does not overdose on bromide; otherwise, they can't go back to chlorine without drain/refill. I've written about a possible test using ammonia and an ammonia test since monochloramine shows up as CC and in an ammonia test, but monobromamine should show up as FC instead. So adding an amount of ammonia in the same molar amount as chlorine or bromine could be used as a test.

 

[JamesW]

Yes, but with an SWG there's really no point in turning a chlorine pool into a bromine pool. This thread is about having a pool with very high CYA turn into a bromine pool. Presumably a pool with an SWG shouldn't have a very high CYA since one shouldn't be adding Trichlor or Dichlor to it.

What I meant was in a situation where someone had been using tabs and the CYA got too high, they could convert to a SWG by adding regular salt and just enough sodium bromide to ensure that any chlorine produced would become bromine.

 

[chem geek]

OK, that make sense.

 

[Tepelus]

Bromine is sensitive to UVB. It make sense to use a solar cover. It will prevent the bromine depletion and will reduce a lot the amount of sanitiser requested for proper pool sanitation. I am maintaining a pool with bromine in the South of France and the solar cover makes a big difference.

 

[chem geek]

Yes, that's true even for chlorine as well. I use a lot less chlorine in my pool due to a mostly opaque cover. On the other hand, chlorine oxidizes the cover itself so the chlorine demand does not drop as low as one might expect. With no bather load and the cover on all the time and at 88ºF water temperature, I have a roughly 0.7 ppm FC loss when the FC/CYA ratio averages 10% (I generally go from 3-6 ppm FC with 40 ppm CYA).

What is your 24-hour bromine usage with the cover on and no bather load and at what water temperature? Though bromine is less reactive than chlorine, it also isn't moderated in its strength by CYA so I'm not sure where that ends up with regard to bromine oxidation of pool covers.

 

[Tepelus]

Current water temperature is 84. The thermal blanquette is not affected by the bromine at all - until now. Has been in use one year and has been in contact with water most of the time. My UV lamp generates a small amount of bromine (0.5 - 1ppm) keeping the water clear all year in combination with 1ppm Cu. I do increase bromine with bleach or with some trichlor pucks when I open the pool. Ph is kept at 7.3 by the Ph controller. When the pool is in use I need about 1ppm beach or a puck every four days.

 

[chem geek]

OK, with the low target bromine level and use of the blanket, your usage is low and reasonable even though your usage is nearly 100% of the target level (i.e. 1 ppm), but you have your UV system to sort of maintain a bromine level. Probably those not using a cover and in full sun might find bromine to be more of a problem.