How can I test Bromine levels?

[Matt]

I've had a Cl based pool with a SWG for a few years now and have had no trouble with that. I use a Taylor K-2006 for testing.

I now have to figure out how to balance a spa. This spa specifically prohibits the use of Cl (although I assume that refers to hypochlorous acid and not Cl- ions). I understand the idea of creating a reserve of Br- ions in solution and then using some type of oxidizing agent (bleach, trichlor/dichlor, potassium monopersulfate, etc.) to generate the actual hypobromous acid sanitizer.

My problem is that I do not see any test kits that give me the info I need. It seems that I would need to test for 1) sanitizing bromine (hypobromous acid), which is what I believe the DPD test does (multiplied by 2.25 since it's calibrated for Cl) and 2) Br- reserve bank concentration. I intend to start up the spa with some NaBr and then oxidize it. If my DPD test comes back low, how do I know if I need to add more Br salts or if I just need to oxidize existing Br? Is it possible to get a good test for Br- ions in addition to the DPD (which as I understand it tests for hypobromous acid)?

Thanks.

 

[Butterfly]

Hi Matt,

Here is a sticky by Waterbear, "How to use bromine in your spa......." that should help get you started:

http://www.troublefreepool.com/viewtopic.php?t=102


Welcome to the forum :lol:

 

[Matt]

Thanks for that Joyce, but I'm still not sure how I can tell if I have enough Bromine reserve in the pool to add an oxidizer to regenerate the sanitizing hypobromous acid, or if I need to replenish the Br first. Any idea how to figure this out?

Thanks.

Matt

 

[Guest]

IF you added sodium bromide on each filling (1/2 oz per 100 gallons) and you change the water every 3-4 months then you are good to go. If you didnt' then maybe or maybe not.
One way to check is to shock with MPS (NOT chlorine) then test for FC with DPD and multiply the results by 2 to get bromine levels.
If your bromine is at shock level ( above 10 ppm) then you have enough of a bromide reserve in the water. IF the bromine level doesn't rise much then you don't have enough of a bromide reserve.
This is not foolproof and the BEST way is to add the sodium bromide on each fill.

 

[CaOCl2]

Is it possible to get a good test for Br- ions in addition to the DPD (which as I understand it tests for hypobromous acid)?
Thanks.

Just out of curiousity I looked it up.

It seems testing for Br- involves … phenol red!

"When a sample containing bromide ions (Br-) is treated with a dilute solution of Chloramine-T in the presence of phenol red, the oxidation of bromide and subsequent bromination of the phenol red occur readily. If the reaction is buffered to pH 4.5 to 4.7, the color of the brominated compound will range from reddish to violet, depending on the bromide concentration." -- Standard Methods, 17th ed.

Cool eh? And there I was thinking phenol red was only used for pH !

I don't know of any kits that tests for bromide though, all I've seen are bromine.

 

[Matt]

Thanks to both of you.

I did open the spa with a little packet of Brom-Start (it's 2 oz. of NaBr salt, solid). Basically, I put in new water, balanced total alk (~120) and then pH (~7.6), and then added the NaBr. Waited a few minutes and added a packet of the potassium monopersulfate shock and the bromine levels went up from about 4 to 14. (The active Cl in the tap water must have oxidized some of the Br before the shock was added, as we have about 4 ppm Cl in our tap here.)

I was concerned that there would be depletion of Br over time. It sounds like this is a non-issue unless one has extreme splash out or waits a very long time (over 3 months) between changing water. I know sunlight supposedly causes Br loss, but from what you're saying all it does is convert active Br to inactive Br, not actually remove any Br from the spa.

I looked for tests that would show Br levels too but never found any.

Also, it's a fiberglass spa. Is there any need to worry about Ca hardness with that, or can I just leave it as it is in the tap water?

 

[Guest]

Thanks to both of you.

I did open the spa with a little packet of Brom-Start (it's 2 oz. of NaBr salt, solid). Basically, I put in new water, balanced total alk (~120) and then pH (~7.6), and then added the NaBr. Waited a few minutes and added a packet of the potassium monopersulfate shock and the bromine levels went up from about 4 to 14. (The active Cl in the tap water must have oxidized some of the Br before the shock was added, as we have about 4 ppm Cl in our tap here.)

I was concerned that there would be depletion of Br over time. It sounds like this is a non-issue unless one has extreme splash out or waits a very long time (over 3 months) between changing water.
Exactly!
As long as shocking raises the bromine level you are fine, also if you are using bromine tabs in a floater you are also adding bromide ions to the water as the tabs dissolve.
I know sunlight supposedly causes Br loss, but from what you're saying all it does is convert active Br to inactive Br, not actually remove any Br from the spa.

I looked for tests that would show Br levels too but never found any.
It's not really needed.
Also, it's a fiberglass spa. Is there any need to worry about Ca hardness with that, or can I just leave it as it is in the tap water?

Depends on what the hardness of the tap water is. Soft water will foam more readily than hard water and spas are notorious for foaming because of the small water to bather ratio and all the aeration from the jets. If your CH is below about 150 I would raise it to at least that level.

 

[Matt]

The problem is that when you do a FAS/DPD Cl/Br test, you cannot tell if the pink is from bromine or chlorine, you can only tell that you have active sanitizer. Thus, if you shock with a half cup of bleach, and you then test for sanitizer, it will be positive whether or not you have a bromine reserve. You can use the potassium monopersulfate shock (I actually used a packet this fill), and that should show no sanitizer if you have no bromine bank (or a reduced sanitizer level <10 if you have insufficient bromine bank). I'd prefer to be able to just use the chlorine bleach as a shock as it is cheaper and easier to get.

I guess though that it sounds like I don't really need to worry about it as long as I'm changing water ever 3 months or so (it's not a high bather load, rarely more than 2 people, almost always family, and sometimes a week or more w/o use). No little kids so not a lot of splashing and such.

I suppose if I did keep water in longer, I could just make sure I add a bromine packet every couple of months to be sure, or some of the combined sodium bromide / oxidizer powder I have.

 

[Guest]

Don'tkeep the water longer than 3-4 months. There are reasons but the chemistry is a bit intense so I don't have time to go into it right now since I am about to leave for work.

 

[Matt]

If you get a chance later, I'd be curious as to why. I'm a biochemist by trade, and have training in physical and inorganic chem as well, so I always like to understand the chemistry so that I can better control/manipulate it.

 

[Guest]

Well, then the chemistry is not going to be intense for you at all!
In a nutshell, you will get a buildup of undesirable TDS in the water (not really a problem for a pool but it can be a problem for a spa because of the use of MPS for shocking and sodium bisulfate for pH control both of which add sulfates.) Also, the bromide reserve in the water (You DID add sodium bromide on filling, didn't you?) does get oxidized to bromates after a while, particularly if ozone is also used in the spa. The bromates cannot be 'regenerated' into hypobromous acid by oxidation like the bromide ions can so you really do need to 'start fresh' every 3-4 months, possibly earlier if you are also using ozone.

 

[Guest]

The problem is that when you do a FAS/DPD Cl/Br test, you cannot tell if the pink is from bromine or chlorine, you can only tell that you have active sanitizer.
If you have sodium bromide in the water you will have hypobromous acid and not hypochlorous acid. That is why you add sodium bromide (1/2 oz per 100 gallons) on each fill.
Thus, if you shock with a half cup of bleach, and you then test for sanitizer, it will be positive whether or not you have a bromine reserve. You can use the potassium monopersulfate shock (I actually used a packet this fill), and that should show no sanitizer if you have no bromine bank (or a reduced sanitizer level <10 if you have insufficient bromine bank). I'd prefer to be able to just use the chlorine bleach as a shock as it is cheaper and easier to get.
If you are testing total bromine (which is what you are supposed to be testing for and not free bromine) then even MPS will show up on testing! However, if you shock with MPS and test Free Bromine you will get some idea of your bromide bank since MPS will not show up on a DPD or FAS-DPD test but only on an OTO test or the DPD/iodide test for total bromine/chlorine. FAS-DPD is certainly fine for testing bromine but it really does not give you the full picture since you are only testing free bromine.
I guess though that it sounds like I don't really need to worry about it as long as I'm changing water ever 3 months or so (it's not a high bather load, rarely more than 2 people, almost always family, and sometimes a week or more w/o use). No little kids so not a lot of splashing and such.

I suppose if I did keep water in longer, I could just make sure I add a bromine packet every couple of months to be sure, or some of the combined sodium bromide / oxidizer powder I have.

 

[Matt]

If you have sodium bromide in the water you will have hypobromous acid and not hypochlorous acid. That is why you add sodium bromide (1/2 oz per 100 gallons) on each fill.

Well yes, and that's the point really. I may know that I added NaBr, but I don't know that it's still there (and there is an ozonator as well, so I will lose some to bromates). It could be lost to splashout, bromates, or something else. If I add a non-chlorine shock, and I have no Br, the test will show no Br/Cl. If I add a Cl based shock (e.g. bleach) then the test will show that I have Br or Cl, but I won't know which. If there's enough Br- in the bank, it will be hypobromous acid, but if there is no Br- present, it will be hypochlorous, and the test cannot distinguish those two. (Or it will be a mix of both if there is enough Br- to make some hypobromous acid, but not enough to use up all the hypochlorous acid.)

If you are testing total bromine (which is what you are supposed to be testing for and not free bromine) then even MPS will show up on testing! However, if you shock with MPS and test Free Bromine you will get some idea of your bromide bank since MPS will not show up on a DPD or FAS-DPD test but only on an OTO test or the DPD/iodide test for total bromine/chlorine. FAS-DPD is certainly fine for testing bromine but it really does not give you the full picture since you are only testing free bromine.

This isn't exactly correct. FAS-DPD tests cannot distinguish between free and total bromine and only tests for the latter (total). The third reagent (KI) which is used in Cl testing is not used in Br testing. DPD will turn a solution pink if 1) there is free Cl or 2) there is free or combined bromine (i.e. bromamines or hypobromous acid). You cannot test for just free Br, because bromamines and hypobromous acid react the same way to DPD (unlike with Cl, where the hypochlorous acid reacts to turn pink, but the chloramines do not).

Here's a quote from the Taylor K-2006 book from this year (p. 31):

Bromine Chemistry: ...
Reaction with DPD: bromamines react with DPD #1 and DPD #2 in a manner similar to both hypobromous and hypochlorous acids. This means combined bromine cannot be distinguished from free available bromine. Consequently, you only test for the total bromine residual. (See pages 43-44 for recommendations.) For this reason, there is no need for DPD #3 in Bromine test kits.

For reference:
DPD #1 = Taylor R-0870 = DPD (N,N-diethyl-p-phenylenediamine) powder
DPD #2 = Taylor R-0871 = FAS (ferrous ammonium sulfate)
DPD #3 = Taylor R-0003 = KI (potassium iodide)

So when you do a bromine test with the FAS-DPD methodology, you are testing for both free bromine (hypobromous acid) and combined bromine (bromamines) at the same time. Then you titrate with the FAS to colorless and that tells you how much bromine (total) or chlorine (free) you have. (The conversion factor is different for Br, take the reading as if it were Cl and multiply by 2.25.) With Cl, you can then add the KI, which will cause the mixture to again turn pink, and titrate down with the FAS to get your chloramine levels.

The reagents R-0871 and R-0872 are both ferrous ammonium sulfate, but they are in different concentrations, as the conversion ratios are different for Br and Cl. You can, however, use either to test Br or Cl if you multiply by the correct ratio. Having the right bottle for your sanitizer saves a calculation.

OTO also gives a total bromine level (sum of hypobromous acid and bromamines).

From the Taylor K-2006 book p. 45:

4. Can I use a bromine comparator to test a chlorine sanitized pool?
Yes. DPD and OT undergo the same reaction with bromine as with chlorine, but the color intensities produced are different. To convert from bromine to chlorine, simply divide the value on the bromine comparator by 2.25. If a chlorine comparator is used to test a bromine sanitized pool, multiply the result by 2.25 to determine ppm bromine. Note: Taylor offers comparators with dual sanitizer values, so you can measure either chlorine or bromine without doing a conversion.

 

[Guest]

Not completely true to the best of my knowledge. My understanding is that the wurster dye (pink color from the reaction with DPD) only occurs with free chlorine and free bromine and I have seen this at work when we test bromine systems. We use Lamotte chemistry and colorimeter and they have separate tests for free and total chlorine or bromine and I get lower readings on the free bromine than the total bromine consistently. The dry reagent used for the total bromine/chlorine test does contain the iodide salt in addtion to the DPD.
In fact, they way the combined chlorine test works with the FAS-DPD test is the potassium iodide is added and it is oxdized to iodine by any chloramines, bromamines, and other oxidizers like MPS or sodium percarbonae that are in the water and the iodine is what reacts with the DPD in the water to produce more worster dye that is then titrated. any free chlorine or bromine has already been titrated with the initial titration. If you have an FAS-DPD test and a bromine system you can verify this yourself. Test the spa after use and before shocking, there should be bromamines present in the water. You should find that adding the iodide solution produces a pink color again much like a chlorine system when chloramines are present. Since this test will also be sensitive for ozone (DPD/iodide is one of the colormetric tests for ozone) you might want to turn the ozonator off the make sure it is not oxidzing the bromamines and also not interfering with the test results.
Likewise, with DPD testing, except that you will have a total sanitizer/oxidizer reading because ALL the oxidizers in the water react to convert the iodide ions to iodine, which then produces the wurster dye with the DPD.

 

[Matt]

While your ideas seem plausible, they are exactly the opposite of what Taylor says. I can't say I really understand the reactions and mechanisms in great detail on the FAS-DPD test. Maybe I'll see if I can call Taylor.

EDIT: I just looked on the Taylor site and the Cl and Br test kits both contain the same DPD powder, R-0870. They also use the same titrant (FAS), although in differing concentrations to make the tests convenient. None of the bromine tests use the iodine salts.

 

[Guest]

While your ideas seem plausible, they are exactly the opposite of what Taylor says. I can't say I really understand the reactions and mechanisms in great detail on the FAS-DPD test. Maybe I'll see if I can call Taylor.

EDIT: I just looked on the Taylor site and the Cl and Br test kits both contain the same DPD powder, R-0870. They also use the same titrant (FAS), although in differing concentrations to make the tests convenient. None of the bromine tests use the iodine salts.

Correct, they are testing free bromine. Taylor does have some inaccuracies in their info. They are not the final word. You stated that you are a chemist (or biochemist) I am suprised that you have taken some of the things they said at face value and also that you didn't realize that the EDTA titrant in the calcium harndess test (from your calcium thread) was a chelating agent.

 

[Matt]

I'm familiar with EDTA and its use in chelation, but I honestly never paid attention to how the calcium hardness test worked or what the reagents were.

I get the same results with an OTO test and a DPD test on bromine, and OTO definitely cannot distinguish free halogens from haloamines, suggesting that you are in fact testing bromamines + hypobromous acid with the DPD. Chemically, it makes more sense that you are testing for total bromine, not free bromine. Besides, unlike chloramines, bromamines are known to be good sanitizers. I think Taylor is correct here. If it were necessary to test for free bromine separately, I'm sure at least one of the test companies would provide a means of doing that, but every one I've seen describes the DPD test and the OTO test as total bromine.

 

[Guest]

I think I test a few more pools and spas than you do in a day's time. There is a difference in the DPD and DPD/iodide tests when testing bromine when there are organics in the water. If there is an ozonator then there won't be as much of a difference since the ozone is in effect oxidizing the organics before they can form bromamines. (this IS the purpose of the ozone after all). When you say that bromamines are good sanitizers you are just repeating one of those myths in pool care that is accepted as truth. There is evidence to the contrary and bromamines do contribute to the 'bromine smell' that many find objectionable in a bromine spa. (another myth that is accepted as truth in the pool/spa industry is that you lower pH by walking acid around the pool with the pump running and lower TA by slugging it with the pump off. Even Taylor says this and it is just plain wrong. It has been debunked several years back in the JSPSI yet it still is repeated over and over again even though if you look at it chemically you can see that it just doesn't make sense (Try these links for more info:
http://www.troublefreepool.com/viewtopic.php?t=1089
http://www.troublefreepool.com/viewtopic.php?t=4979)
Another bromine myth is that bromine cannot be stabilized against destruction by UV light but if you are using organic bromine iwth a dimethyhydantoin carrier (in other words, bromine tabs) this is not true. The dimethylhydantion does form bromine compounds that do not break down in UV light.
Much of the bromine 'information' that is constantly repeated in the pool industry comes from the late Jock Hamilton of United Chemical. He is the same one that came out with the 'Hamilton Index" for water balance that involves running, among other things, at a pH of around 8.0 that has no basis in scientific fact but is based entirely on empirical evidence (United Chemical even admits this).Interestingly enough the majority of United's products are sodium bromide based and function more effectively at a pH of around 8.0! Could marketing have come into play here? He is the one that came up with bromamines being just as effective a sanitizer as hypobromous acid because many of United's sodium bromide products are sold as algaecides. Bromamines are an effective algaecide because, being a nitrogen compound it will be consumed by algae as a food source and then kill the algae. Monochloramine is equally effective which is why an old method of killing algae was to add anhydrous ammonia to a pool with the pH adjusted to above 7.8 to favor the production of monochloramine. Hasa (the manufacturer of the Liquidator and also a manufacturer of soidum hypochlorite) STILL sells anhydrous ammonia for this purpose and there are many inorganic ammona/EDTA and quaternary/EDTA products on the market (often with the word Yellow in their names) that are also used in a similar manner to form monochloramine to kill algae.
The point of all this is just because Taylor says it's true doesn't necesssarily make it true and this becomes very evident once you have a bit more background in the pool industry and where it's 'truths' actually come from.

 

[Matt]

Any scientist should remain open to any possibility until it is proven otherwise. If you can offer me some convincing chemistry or other evidence (like a link to a scientific paper, proposed reaction mechanisms, or an experiment that I can perform) as to why Taylor is wrong about the DPD test, I'm all ears.

The point of all this is just because Taylor says it's true doesn't necesssarily make it true

Taylor making a claim in itself doesn't make anything true, but I have good reason to believe that they have some pretty talented chemists there, and that they are more often right than wrong. That being said, I'm open to the possibility that they are wrong, but I'd need some solid science to believe that they and all the other test kit manufacturers are wrong.

 

[Guest]

well, for one LaMotte has different info on DPD testing for bromine (I use LaMotte UDVs and colormeter at work and back up certain tests with Taylor chemistries because of inherent range limitations in the colormetric tests LaMotte uses vs. the titrations that Taylor uses. LaMotte is every bit as respected in water testing as is Taylor for many industries, not just pool and spa. LaMotte uses separate UDVs (unit dose vials) with dry reagents that 3 ml of water to be tested is pipetted into for each test. They have separate tests for FC and TC. For testing bromine they say that either can be used but the TC vial can read higher levels since it will give readings for total bromine and, in fact, when I test a bromine system I use both UDVs since this gives me an indicator of whether the bromine system needs shocking (unless MPS is the oxidizer being used since this will show up on the TC test and give a false high reading).
As far as an experiment to perform I already suggested one. Turn of the ozone, use the spa to develop bromamines in the water and test with DPD and then DPD/iodide.
As far as a test for sodium bromide itself, Hach has a reverse titration strip under the AquaChek brand that tests for sodium bromide in the same way their sodium chloride reverse titration strips work but it is designed to test much higher levels in a spa using a sodium bromide based bromine generator such as the Genesis unit. This works in a similar way to a SWG but it does not use any sodium chloride to first generate chlorine which then oxidizes a smaller amount of sodium bromide into hypobromous acid but directly converts a much higher level of sodium bromide into hypobromous acid by electrolysis. It will not read the very low level used to create a bromide bank in a standard bromine system.