Bromine Obsolete in pool

[123]

Having a major problem:

Bought some sodium perborate and added to pool thinking that it would shock the water and raise my Bromine lvl. Tested 30 minutes after shocking to find that my DPD test showed 0 Br reading.

Thought that the perborate might have bleached out the colour of my DPD i then tested the water by adding 2 - 3 drops of sample into vial with tap water again the test failed to show any slightest of colour.

I also noticed that my water started to cloud. I was using PMS before i switched and my DPD test always showed some colour before colour gets bleached.


Can anyone tell me if adding Sodium perborate is okay? And do i have any Bromine left in my pool or has the test just bleached out? And if my test has bleach outed what can i do to test my Bromine levels?

 

[Melt In The Sun]

Honestly, I've never heard of sodium perborate, and it doesn't sound like it would have anything to do with bromine. Perhaps you meant sodium perbromate? Not that I've ever heard of that being used in a pool either...

Someone should be along to help you soon!

BTW...PMS may be shocking, but I presume you meant MPS

 

[CaOCl2]

Is is sodium perborate or sodium percarbonate? Sodium percarbonate will dechlorinate pool water.

 

[JasonLion]

Sodium perborate is an oxidizing agent, similar in some ways to MPS. It is almost never used with pools or spas, so I am not familiar with what effect it would have on bromine.

I would try adding some chlorine and then check to see if you have a bromine level after that.

 

[123]

I presume i have done the wrong thing then. When you say adding some chlorine you mean adding chlorine into the sample water and testing if i hold a DPD reading?

I thought it should have been something similar to percarbonate in its effect...?

 

[Ohm_Boy]

I think that chlorine should be added to the pool. Chlorine is used as a Bromine activator, to re-create the bromine reserve. I'm no bromine whiz, though, so we should get confirmation from one of the smart guys.

 

[257WbyMag]

I think that chlorine should be added to the pool. Chlorine is used as a Bromine activator, to re-create the bromine reserve. I'm no bromine whiz, though, so we should get confirmation from one of the smart guys.

That's the way that I understand it. Once a bromine pool, always a bromine pool, or so I'm told. Add a chlorine source and you'll get more bromine.

Paging chem geek to tell us why.

 

[123]

Any help would be great, pools is getting worse as i speak. I thought that the perborate would have hydrolized into h202 which should have converted my bromide into hypobromus acid.

Any advice would be most appreciated.

 

[mamasproject]

I was told by my pool builder...who pushes Bromine in his pools that you can convert a Bromine pool to a Chlorine pool but you can't go the other way. My neighbor uses Bromine and does not put chlorine in her pool. Just thought I'd chime in here!

And Bromine is EXPENSIVE!!!!!!! That's whey we went with chlorine! :-D

 

[Melt In The Sun]

If you haven't already, see http://www.troublefreepool.com/how-do-i-use-bromine-in-my-spa-or-pool-t102.html

Sounds like adding chlorine to your pool is the way to go.

 

[chem geek]

If the pool was using bromine for some time or if it started out with sodium bromide added to it, then there should be a bromide bank in the water. That is, there should be bromide ions in the water. When you add an oxidizer such as chlorine or non-chlorine shock (MPS) to water that has bromide in it, the bromide gets oxidized to become bromine while the oxidizer you added gets used up (i.e. chlorine becomes chloride salt).

Sodium perborate added to water becomes hydrogen peroxide and borate as follows. The typical chemical formula of NaBO₃•H₂O does not reflect its actual chemical structure which is really a perborate dimer with peroxide bonds (see here).

B₂O₄(OH)₂^2- + 4H₂O ---> H₂O₂ + 2B(OH)₄^-
Perborate Ion + Water ---> Hydrogen Peroxide + Borate Ion

Hydrogen Peroxide is both an oxidizer and a reducing agent in the presence of strong oxidizers (it can go both ways via two different chemical reaction paths) so effectively adding sodium perborate is like adding sodium percarbonate in that both will result in dechlorinating or debrominating water. The following are two paths for hydrogen peroxide:

H₂O₂ + 2H⁺ + 2e^- ---> 2H₂O ..... E₀ = +1.776V
H₂O₂ ---> O₂ + 2H⁺ + 2e^- ..... E₀ = -0.695V

so with the bromine reaction:

HOBr + H⁺ + 2e^- ---> Br^- + H₂O ..... E₀ = +1.331V

the net result is:

H₂O₂ + HOBr ---> O₂ + H⁺ + Br^- + H₂O ..... E₀ = +0.636V
..... -or-
H₂O₂ + Br^- + H⁺ ---> HOBr + H₂O ..... E₀ = +0.445V

Either of the above two reactions is possible. Which one occurs depends on activation energies which determine the reaction rates and I don't know what those are.

If the hydrogen peroxide mostly debrominates the water, then since there may be hydrogen peroxide leftover in the water, it may take quite a bit of chlorine to add before chlorine or bromine will start registering. As I indicated before, if there are bromide ions in the water, then if you start measuring a chlorine/bromine level, it's really bromine.

Richard

 

[123]

I thought h202 only reduced chlorine whereas if bromine it would have been the reverse with an increase in Br lvl? May i ask why the same did not happen when i added PMS? With PMS i always registered with a higher bromine reading...

Why would percarbonate be sold as a shock if its going to reduce readings in a non chlorine pool?

Should i be avoiding H202 and related products altogether next time i shock?

 

[chem geek]

I suppose that in the bromine situation it can go either way since it could oxidize bromide to bromine, but can also go the other way. I don't know the activation energies for the two reactions so don't know the reaction rates which would determine which way it goes.

One does not use percarbonate as a shock in pools. If it is used, it will dechlorinate the water. It is an oxidizer that is typically used for a faster conversion (oxidation) of Baqua pools as the higher hydrogen peroxide levels combined with higher pH make that conversion more rapid. If it is being used in chlorine pools, then it's just a temporary alternate oxidizer, but you have to add chlorine back to the pool. In fact, on another spa forum, hydrogen peroxide is actually used to intentionally dechlorinate if one has too high an FC level.

Generally speaking, I would not use percarbonate, perborate or hydrogen peroxide in either a chlorine nor a bromine pool/spa. It should only be used as an oxidizer in a Baqua/biguanide/PHMB pool though at reasonable levels (if too high, it will oxidize Baqua itself too quickly).

 

[123]

Iv been using bromine for a good 3 -4 months now so i should have bromide ions.... if i am following what youv said my pool should have no bromide for the h202 to reduce the H0Br to nothing. My pool should still look and stay clean however even i dont register bromine since i have H202 in my water right?

Last but not least next time i shock i should really should be adding some sodium bromide into the pool then?

 

[chem geek]

No, even if you had bromide ions, it doesn't mean that the hydrogen peroxide will oxidize them. It might oxidize some to bromine and then immediately reduce them back to bromide ions. Or if there is already some bromine, it might reduce it to bromide ions first. Again, I can't tell which way it will dominate, but it doesn't seem like a good idea to me to use hydrogen peroxide with bromine unless one is certain that the oxidation of bromide to bromine is the clearly faster reaction path.

 

[123]

Is this also true for Monopersulfate? What can i do next time to shock without having downtime/ waiting for my Br lvls to return back to the norm?

From time to time my water losses its lust nad hence the shocking...

 

[chem geek]

Monopersulfate, like chlorine, is only an oxidizer and will not act as a reducing agent. So either chlorine or MPS can be used to shock a bromine pool/spa to generate more bromine from the bromide ions.

 

[123]

Two more questions:

(1) How much chlorine should i be looking at adding? I added around 4 lbs of perborate
(2) With no Br and some h202 in the pool my water should stay clear right? Or can it still cloud and go worse?

 

[chem geek]

Can you tell me whether your perborate was "sodium perborate monohydrate" or "sodium perborate tetrahydrate"? Or is there a percentage of sodium perborate on the ingredients label and if so I need to know not only the percentage but the exact chemical name that is lsted (including any ...hydrate).

If there is leftover hydrogen peroxide, then this might keep the pool from turning cloudy from bather waste, though hydrogen peroxide isn't great at preventing algae except at higher concentrations. So the pool might still turn cloudy from algae growth though that will take a day or two to develop.

If the sodium perborate was monohydrate, then this is (4 pounds perborate) * (70.9064 g/mole chlorine) / (99.815 g/mole perborate) / (2 perborate per hydrogen peroxide) = 1.4 pounds of chlorine gas equivalent. That's around 1.3 gallons of 12.5% chlorinating liquid. This assumes that none of the hydrogen peroxide got used up -- if there was bromine in the water, then some of the hydrogen peroxide may have been used up. So think of this 1.3 gallons as a worst case scenario and it might require less chlorine before you get a reading.