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How To Switch To Chlorine From Bromine In Pool


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#1 delgriffith

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Posted 06 May 2008 - 09:21 AM

Got a 27ft round above ground pool. Used Bromine since we got the pool 3 years ago. Too much money to continue!! Was talked into bromine by the pool guy and regretted ever since. Want to switch to chlorine, pool is half empty right now. Want to get it opened up this week and would like to make the switch if it's feasable. Any help would be appreaciated.

#2 chem geek

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Posted 06 May 2008 - 05:04 PM

The short answer is that you may have to replace your water to convert a bromine pool to a chlorine pool as described here. Have you only used sodium bromide that was then shocked with non-chlorine shock (MPS)? Or have you been using bromine tabs (either BCDMH or DBDMH)? If the former, then shocking with chlorine and exposing the pool to sunlight will get rid of the bromine (some of it will break down in sunlight to bromates instead of bromide). If you used bromine tabs, however, you won't be able to get rid of the bromine nearly as fast without dilution (drain/refill) as the DMH from the tabs will interfere with getting rid of the bromine and is why some say "once a bromine pool; always a bromine pool".

#3 Strannik

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Posted 07 May 2008 - 04:46 AM

If you already have half of it drained best would be to drain completely, refill with fresh water and start from scratch smile.gif
TD Consulting - Distributor of AutoChlor Salt Water Chlorine Generators.
Experts in Salt Water Chlorination.

#4 locust43

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Posted 10 July 2008 - 03:19 PM

You can buy some Baquacil Chlorine/Bromine neutralizer. That's what I did to neutralize the Chlorine in my pool before switching to Baquacil. It says it neutralizes Bromine as well.

#5 chem geek

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Posted 10 July 2008 - 06:58 PM

QUOTE(locust43 @ Jul 10 2008, 04:19 PM) <{POST_SNAPBACK}>
You can buy some Baquacil Chlorine/Bromine neutralizer. That's what I did to neutralize the Chlorine in my pool before switching to Baquacil. It says it neutralizes Bromine as well.

Neutralizing bromine is not the same as getting rid of it. It just converts it to bromide. For a Baqua pool that's OK, but for a chlorine pool you can't have any bromide in it since it will just get converted to bromine by the chlorine and the chlorine will get used up. Actually, even in a Baqua pool I'm surprised you can have bromide in it since shocking with hydrogen peroxide I would think would convert the bromide to bromine as well.

#6 playa7seven7

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Posted 18 August 2008 - 03:30 PM

Hello. I am new to the forum, and have a similar situation to that of the original poster. Sorry in advance for the long post! The "background info" section can probably be skimmed through quickly (or skipped), it is the "questions" section that contains the important stuff...

Background info:
I'm a new homeowner (as of January) of a house that has an in-ground, 18x38 vinyl lined pool. We opened it this spring and the pool guys we hired to help us told us to add bromine as a sanitizer (we have a Hayward "chemical feeder", that they kept referring to as a "bromine feeder")... at this point we did not know that bromine was an alternative to chlorine (a much more expensive alternative at that!), as we had never owned a pool. We also did not know that once a bromine pool, always a bromine pool --I know, should have researched, but we'd been very busy and figured the pool guys we were paying would give us proper guidance.

Well, halfway through the summer, I began questioning why the pool guys told us to add bromine, as we have a "chemical feeder" that accepts either chlorine or bromine. After going back to the guys, they had no explanation other than they thought it was a bromine feeder, so figured it was a bromine pool --also, we were told it was our fault we added bromine, and should have known what chemicals were used in the pool previously; so, we were stuck with the high bromine costs. BTW, I think they automatically figured it was a bromine feeder because Hayward used to only make bromine feeders (not that it really lets them off the hook, as they are the "pros").

To make things more interesting, about one month ago, we were finally able to get in touch with the previous owners, who were able to give us a bit of chemical background info on the pool. We found out that it had been a bromine pool, until last year when they could not afford bromine, so just used chlorine instead. They justified this is OK to do, as long as you don't use both at the same time --I know, not really OK to do...

Anyways, so far we have gone through two 50 gallon buckets of bromine this year (we are trying to milk the last of our bromine so we don't need to buy anymore), which has cost twice as much as it would have for chlorine, and we are investigating the option of trying to convert it to chlorine. In talking to the pool guys we had hired (who we now have a severed relationship with, as they accused us of the wrong-doing, and lying), they briefly mentioned a conversion process of turning a bromine pool into a chlorine pool. So, I was wondering if people have anything they could add to what little they told us:

They said that next spring, we will do a dilution process (to reduce bromide salts), since we can not fully drain it because of the risk of the liner popping up. They said that first, we'll add the typical two feet of fresh water, since we'll drain it two feet for the winter closing. But, then we will then drain it another two feet right after filling it, in which we'll then add another two feet of water. At this point, we'll then add chlorine to the pool, and then begin water sampling/testing for bromide salts. We may then have to drain some more, and then refill.

Questions:
One of my major questions is, what would happen if we decided to do what the last pool owners did, and just start using chlorine next spring after we open up the pool? I realize that since bromide salts are in the pool and if chlorine is added, bromine is regenerated, but this seems like a good thing. Would we experience cloudy, gross water if we simply started adding chlorine (the previous owners claim the water was gorgeous even after using chlorine)? Would we have to use tons more chlorine than we typically would if it had always been a chlorine pool? Right now the water is crystal blue, and I would hate to mess it up next year, as we have really enjoyed it... but the price difference between bromine and chlorine is ridiculous.

The cost of water, and time of having to partially drain and refill a few times would totally negate the cost of another summer's worth of bromine IMO, but I do not see anywhere on the internet that states a step-by-step process of this...I just keep seeing the cliched "once a bromine pool, always a bromine pool" everywhere. I know we'll be replacing the liner in a few years (hopefully it gives us around 3-5 more years of use), in which we'll then have the opportunity to use chlorine, but I think if we do the conversion next year, we'd save hundreds of $$ in the end.

Lastly, I am guessing it will take more than two partial drainings and refillings in order to significantly reduce the amount of bromide salts (draining two feet will reduce the salt concentration by around 30% each time). But, would even reducing the concentration of the salts by 75% (probably around 4 drain-and-refills) do enough to reduce the negative effects of adding chlorine to a previously brominated pool? I think to get the salt concentration down to 5% I would have to perform 8 or 9 drain and refills (around $280 worth of water, and lots of time!), but again, I think it would be worth it in the end, financial-wise.

So, if I could have one question answered in this post, the one that would be most helpful to me is: Is there a certain level that the salts could be dropped down to, in which their presence would not affect the pool chemistry too much once chlorine is added?

Thanks for the help!

Thanks for any input and sorry for the LONG post!

#7 chem geek

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Posted 18 August 2008 - 04:13 PM

It is not "bad" to add chlorine to a bromine pool -- it's not that bad things will happen. It's just that adding chlorine does not turn your pool into a chlorine pool -- it remains a bromine pool. The chlorine simply activates the bromine (it converts the bromide salt into bromine) the same way any oxidizer would do, such as adding the non-chlorine shock MPS to the pool, and the chlorine gets used up in the process getting converted go chloride salt. Technically speaking, if you use BCDMH tablets, you are adding both bromine and chlorine anyway. By only using chlorine alone, you at least stop building up the bromide bank with the hope that over time the bromine will go away (via some diversion to bromate or some outgassing as bromine or hypobromous acid).

HOCl + Br- ---> HOBr + Cl-
Chlorine + Bromide ---> Bromine + Chloride

The main problem with bromine in an outdoor pool, other than the cost, is that it is not protected from breakdown in sunlight. So you end up using more chlorine to reactivate it on a regular basis. This isn't bad -- it's just costly and annoying.

One thing that can be done that I haven't heard people doing is to add Cyanuric Acid to the water. Bromine will not combine with CYA so you won't get any loss of disinfection nor direct protection of bromine by attaching to CYA, but you will get some protection of bromine from breakdown in the lower depths of water as the CYA itself will absorb the UV rays from the sun shielding the bromine at lower depths. This could help you lower your chlorine usage by slowing down the breakdown of bromine in sunlight. Having CYA in the water will lower the effective chlorine concentration so might slow down the reactivation of the bromine, but that shouldn't be a problem since you'll have some chlorine around instead. Your sanitizer test measures total chlorine and bromine together so you really can't distinguish between the two anyway (unfortunately).

So you can certainly use chlorine instead of bromine since the worst thing that happens is that your usage is higher than it would be if it were a pure chlorine pool. It's really too bad that chlorine vs. bromine isn't distinguishable on the chemical tests since the only way you'll have any idea of which you've got is on the amount of usage during the day when the pool isn't used (i.e. no bather load). If you have 30-50 ppm CYA in the water, then if the pool were a chlorine pool then you should lose less than half the FC per day -- at higher CYA or in less sunny areas it's less than 1/3rd of the FC per day. If the pool is a bromine pool, then the loss will likely be higher. Just be sure and keep the FC reading of chlorine at least at 7.5% of the CYA level (the bromine reading is 2.25 times higher though most measuring kits just show 2 times so if the reading is on the bromine scale, then have that be at least 15% of the CYA level). If you want to use lower levels, then you'll need a supplemental algaecide (PolyQuat 60).

Richard

#8 playa7seven7

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Posted 18 August 2008 - 06:06 PM

Thanks for the quick response! I guess I won't be too worried about side effects occurring from adding chlorine. I still plan on doing some partial draining & refilling, but maybe not to the extent I had planned on.

Since I have never used CYA or chlorine, I am sure I will have more questions in a couple weeks when my bromine runs out (if the weather is still warm enough to swim), otherwise, it'll have to wait until next spring.

Thanks again for the help.

#9 Mark357

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Posted 26 August 2008 - 04:07 AM

My advice for anyone converting from using bromine to chlorine is to just start using chlorine. It usually works just fine. The pool will continue to be bromine for a while. Although the bromine does break down faster in sunlight than stabilized chlorine, it is relatively easy to maintain a steady 2 to 4 ppm of sanitizer. Just use a trichlor feeder set on low to provide a low continuous dose of about 0.50 ppm per day and add enough bleach each day to keep the sanitizer level at a steady 2 to 4 ppm. Once the stabilizer reaches 60 stop using the trichlor tabs and just use bleach. Or you could add 30 to 60 ppm of stabilizer right away and just use bleach everyday.

Anyone using bromine should never just use bromine tabs anyway. The DMH (dimethyl hydantoin) builds up and causes problems. Once you have established a low level of bromine you should use mostly chlorine (at least 90%) as it will become bromine anyway. The best way to use bromine is to maintain the lowest possible bromide bank. Ideally, the bromide bank should be low enough so that when you add the chlorine only half is converted to bromine and half stays as chlorine although that is very difficult to do.


#10 Mark357

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Posted 26 August 2008 - 09:47 AM

Here is the formula for Dimethylhydantoin…C5H8N2O2
Here is the formula for Cyanuric acid…….....C3H3N3O3
As you can see they are very similar.
C3H3N3O3 + HOCl <-> H2O + C3H2ClN3O3
Cyanuric acid combines with hypochlorous acid to form a chlorinated isocyanurate. As the hypochlorous acid gets used up the equilibrium shifts and some of the chlorinated isocyanurate becomes hypochlorous acid.

Here is the formula for Trichloroisocyanuric acid………………..(C3Cl3N3O3)
Active Chlorine 45.76% by mass
C3Cl3N3O3 + 3H2O <-> 3HOCl + C3H3N3O3
Every pound of Trichloroisocyanuric acid (C3Cl3N3O3) contains 0.4576 lb of chlorine and the rest is 0.5424 pounds of cyanuric acid. A 35 lb. bucket of trichlor contains 18.98 lbs of cyanuric acid. That will raise the cyanuric by 110 ppm in 20,000 gallons.

Here is the formula for 1-bromo-3-chloro-5,5-dimethyl hydantoin…(C5H6BrClN2O2)
Active Bromine 33.09% by mass
Active Chlorine 14.68% by mass
You are getting the same number of chlorine atoms and bromine atoms; bromine is just 2.28 times as heavy as chlorine. As you can see, the bromine tabs come with chlorine already mixed in, so the chlorine has to be somewhat compatible with the bromine and the dimethylhydantoin.

C5H6BrClN2O2 + 2H2O <-> HOCl + HOBr + C5H8N2O2

This shows that the dimethylhydantoin can build up quite quickly. As in the trichlor tabs, as significant portion of the mass of the product is the carrier.

There is also C5H6Cl2N2O2 (Dichlorodimethylhydantoin) and
C5H6 Br 2N2O2 (Dibromodimethylhydantoin)
C5H6Br2N2O2 + 2H2O <-> 2HOBr + C5H8N2O2

The dimethylhydantoin acts in a similar way to the cyanuric acid although it is not nearly as effective. It is primarily a carrier for the bromine. I think that it's important to minimize the buildup of the dimethylhydantoin. As the hypobromous acid oxidizes something it becomes a bromide ion and it remains in the water until it is reenergized into hypobromous acid. Chlorine is a good activator of bromide ions. If the dimethylhydantoin or the bromide ion levels are too high, sometimes it's best to drain and refill. Most of the time it is not necessary to drain and refill.


#11 chem geek

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Posted 26 August 2008 - 10:25 AM

Mark357,

Do you have any data (equilibrium constants) on DMH with bromine or chlorine? The ones with chlorine and CYA were definitively determined in 1973 and presented in a symposium in 1974 and a book from that symposium (that I have), but I can't seem to find anything on DMH. I don't even know if DMH reduces bromine effectiveness in a similar way that CYA does with chlorine -- that is, which way the equilibrium is shifted with DMH and bromine (or chlorine, for that matter).

I agree that generally you don't want to build up unnecessary organic chemicals in the water, but without knowing the specific chemistry of DMH with bromine or chlorine it's hard to know how much is too much.

Also, do you have any idea how long it takes for a bromine pool to convert over to chlorine? You can read what Ben Powell thought about the situation here including some info from Jock Hamilton.

Richard

#12 Mark357

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Posted 26 August 2008 - 06:42 PM

Richard,

I do not have data related to equilibrium constants. I would suppose that since the DMH does not do a lot to protect the bromine from the sunlight the C5H6BrClN2O2 is probably not a very significant percentage. I would imagine that the HOCl + HOBr + C5H8N2O2 would be the dominant species. It seems that the C5H8N2O2 would probably build up like cyanuric acid. Possibly if the levels were high enough (perhaps over 100 ppm) it would begin to interfere with the chlorine or bromine. I think that as long as the level was low enough it should not cause much trouble. As far as the bromide ions, I am not sure how long they take to break down. I'm not sure what the breakdown mechanism would be. Of course dilution would play a part, but that takes a long time.

What are the equilibrium constants related to chlorine and CYA?





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