Cyanuric Acid, Bromine and Chlorine

[Guest]

Hi - I have some very technical questions.

Cuanuric Acid: Now we all know that Trichlor is highly addictive if you don't keep the CNA under control and it is a case of "The more you use, the more you need!"
I also understand that the CNA surrounds and protects the hypochlorous acid (or is it the Chlorine ION?) from the UV light but does it also protect it from the DPD test.
Lets say there is a real lot of CNA (300 ppm +), you add some TriChlor and test after a few hours. You get a reading of (say) 4 ppm Free Chlorine.
QUESTION: Is this a reading of the total Free (Available) Chlorine or is there more to come that is locked up.

Bromine: This depends a lot on the answer to the question above. Lets say that this is a Bromine pool and the Bromine Bank is properly established. My understanding is that the Hypochlorous Acid, after disassociation from the CMA and in the presence of the Bromine Ion, would produce approx 10 ppm Free Bromine (Hypobromous Acid).
QUESTION: Therefore would the reading really be Bromine or part Chlorine and part Bromine.

Bromine v Chlorine: We have had an 8-year drought and are not permitted to fill pools with a hose-pipe. Because imported water is so expensive, most pools in the area have massive CNA.
We have switched ours to Bromine oxidised with TriChlor, so our CNA is still increasing and we are getting readings of 120 - 600.
QUESTION: Are we heading for real problems? Should we think about oxidising with Sodium Hypochloride or Monopersulphate?

Finally a real stunner. I was testing some water samples for a friend which we took in October. We knew that they had a lot of CNA and the Chlorine/Bromine was high. I left then in clear plastic bottles on a sunny window cill in a heated office (we get a lot of winter sun here in Spain) so that the Chlorine/Bromine would drop.
It was still there in march (5 months later). I wish that I had made proper tests because, in the first few weeks, it seemed to actually INCREASE.
QUESTION: What could have happened here?

[Mike King]

Something went wrong somewhere! I have replied to identify myself!

[dynamictiger]

Cuanuric Acid: Now we all know that Trichlor is highly addictive if you don't keep the CNA under control and it is a case of "The more you use, the more you need!"
I also understand that the CNA surrounds and protects the hypochlorous acid (or is it the Chlorine ION?) from the UV light but does it also protect it from the DPD test.
Lets say there is a real lot of CNA (300 ppm +), you add some TriChlor and test after a few hours. You get a reading of (say) 4 ppm Free Chlorine.
QUESTION: Is this a reading of the total Free (Available) Chlorine or is there more to come that is locked up.

As I understand it, the reading in the presence of CYA is the full amount of chlorine present, not the unbound part at 50 ppm CYA. It is so unusual to see CYA over 150 without the chlorine becoming ineffective I cannot comment on what is happening at 300 or more.

Bromine: This depends a lot on the answer to the question above. Lets say that this is a Bromine pool and the Bromine Bank is properly established. My understanding is that the Hypochlorous Acid, after disassociation from the CMA and in the presence of the Bromine Ion, would produce approx 10 ppm Free Bromine (Hypobromous Acid).
QUESTION: Therefore would the reading really be Bromine or part Chlorine and part Bromine.

The reading is all oxidisers present that react with the reagent in the test kit. So even if you had ozone partially forming this will be included in your reading.

Bromine v Chlorine: We have had an 8-year drought and are not permitted to fill pools with a hose-pipe. Because imported water is so expensive, most pools in the area have massive CNA.
We have switched ours to Bromine oxidised with TriChlor, so our CNA is still increasing and we are getting readings of 120 - 600.
QUESTION: Are we heading for real problems? Should we think about oxidising with Sodium Hypochloride or Monopersulphate?

I am concerned with CYA at the levels you are getting as they could reduce the free available unbound chlorine below 0.5 mg/l. If this occurs certain bacteria may be introduced with the increasing likelihood of potential infection.

I would definitely consider removing the TCCA tabs and adding sodium hypo as the oxidiser. And I'd hope for rain.

Finally a real stunner. I was testing some water samples for a friend which we took in October. We knew that they had a lot of CNA and the Chlorine/Bromine was high. I left then in clear plastic bottles on a sunny window cill in a heated office (we get a lot of winter sun here in Spain) so that the Chlorine/Bromine would drop.
It was still there in march (5 months later). I wish that I had made proper tests because, in the first few weeks, it seemed to actually INCREASE.
QUESTION: What could have happened here?

I am not a chemist, but it is most likely the CYA had bound almost all the chlorine, so it only released a very small amount at a time when the existing chlorine was exhausted. It is possible the chlorine level was seen to increase due to this release phenomenon where by chance you tested during one of these periods (for lack of better explanation) and the chlorine had 'shocked' some combined chlorine back to free. UV also converts combined chlorines to Free so the light may also have played a part.

As for the chlorine residual lasting so long in a bottle in an office the water is protected somewhat from the environment. This leads to a significantly reduced chlorine demand. The very high CYA content slows the chlorine release down and the chlorine only has to deal with algae spores that may be introduced so there is no or very low demand. Temperature must have also played a role as otherwise the water would have evaporated in 6 months. So either the bottle had the lid on or the temperature was pretty close to ideal for the area. If the bottle had its lid on the high CYA and lack of introduced dirt would lead to a chemical demand of 0 or around 0 for all that time.

HTH

[Mike King]

Dear DynamicTiger

Many thanks for that, you have answered everything perfectly and, for your information - Yes, the tops were stoppered on the water samples - so that accunts for it.

If I may prevail upon your time just a little longer, I am extremely worried about you comments regarding high CNA.

Obviously we have to consider draining some of the pools with a really high level but would it not help us if they were all converted to Bromine by adding Sodium Bromide? - or does high CNA also retard the formation of Hypobromous Acid?

I can understand how it would help to oxidise with Sodium Hypochloride as this is not affected by CNA but would using Monopersulphate achieve the same objective? The reason I am asking is because we have MPS tablets available and this would avoid daily visits.

The one pool that worries me in particular is communal to around 250 holiday properties. The capacity is 1,400 M3 (Yes - 1,400,000 litres!), the CNA is currently 600 ppm. It has a very heavy bather load and, from what you say, the risk of infection to bathers is dangerously high.
The pool is scheduled for draining for maintenance work NEXT winter.
Perhaps we should get a qualified chemist to do a proper alalysis, to define suitability for bathing, and make this available to those responsible for the Community.
One solution I can see is to persuade them to install a baulk Sodium Hypo tank with constant feed. Otherwise, would oxidising the Bromine with Sod. Hypo or MPS make it safe for a few months until it is drained?

[dynamictiger]

I usually deal with pools in this volume range normally. I come to sites like this to give back in my small way to the pool industry.

The best bet for this pool is a stream dilution. This is where a specified amount of water is bled off continuously. Using this method the TDS as well as CYA will be reduced. Both of which will have significant impact on chemical demand.

Bromine will not be effected by CYA. It is not affected by sunlight either. However some people are reportedly allergic to Bromine.

Shocking with MPS is probably indicated as I agree it won't be affected by the CYA, however it is likely to increase the sulphates which may damage the concrete long term.

I would strongly recommend a lab water analysis. I normally use a brief water analysis which is conducted by an environmental lab. This test gives the major cation and anion results. THIS REQUIRES TRANSLATION before using it in pools though. CYA test is not included but would be an extra.

Post results here and I'll convert them to TA, CH etc.

In addition and perhaps more importantly I would suggest a bacteriological swab to see if the pool is safe. At 600 mg/l and a high loading it is quite possible the very slow and low chlorine is keeping the water clearish but not safe. This test should include E. Coli, F.Coli as well as any tests your local micro biological lab recommends. In Australia the Health Department do these tests monthly on pools this size.

HTH

[Mike King]

Dear Dynamictiger

I really am most grateful to you for your guidance. Especially so as you are the other side of the world and have nothing to gain.

I intend to follow your advice to the letter. Unfortunately, Summer in the Northern Hemisphere is almost upon us and the most important thing is to do our best right now as few pools can be drained.

There is just one thing that I did not understand. If you could explain, everything will be completely clear, both in the short and long terms.

You said that some bathers have an allergic reaction to Bromine. However, we have been using Bromine in most pools (including the large one) without any complaints and the water has remained clear. On several occasions it BEGAN to deterioate and we shocked with S. Hypo. This cleared the water immediately.
We keep everything else in good order, TA, CH, pH, filtration equipment, regular sweeping etc.
The only doubt I now have: You said that Bromine is not affected by CNA. In this case would we be safe to continue for this summer? Should we have regular Bio. tests as well? Is there anything else we should do?

Thanks again for your time.

Mike

[dynamictiger]

Some people develop rashes from Bromine if it is not an issue in your country, don't worry about it as it may be a skin type reaction.

Bromine should be okay to use as primary sanitiser through the summer. However you may have an issue identifying when it needs shocking correctly. You could consider shocking on a time basis instead of a cloudy basis.

I would invest in monthly bacteria testing or rather ask my client to invest in it.

HTH