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#3270 - 07/31/10 08:46 AM
super-chlorination
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Mal T
Newbie
Registered: 07/31/10
Posts: 2
(202.45.120.97)
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Hi, Im really confused about superchlorination. I work in a pool shop in Adelaide South Australia and have always told my customers to super-chlorinate their pools once per week or fortnight with a 2-4 times daily dose (which accords with what is on the packaging) as a bit of an insurance policy and to avoid problems in the pool. Now I also think I understood combined chlorine and breakpoint chlorination and realise that a 2 times daily dose will raise free chlorine levels by 10ppm which can take care of up to 1ppm of combined chlorine (rarely do I see combined chlorine levels higher than this for backyard pools)
What I am confused about is that one of my co-workers is suggesting super-chlorination dosage rates of 10 times normal daily dose. When I have queried this he has referred me onto the http://www.poolandspa.com website where it does indeed recommend to superchlorinate with 5-10 times the normal daily dose. I have visited dozens of websites and the http://www.poolandspa.com website is the only website I have found that recommends such a large dose in a general sense. Using the worst case of 10 times normal daily dosage my calculations are that in a stabilised pool this dosage would lift chlorine levels to 25pp or to 50ppm in an unstabilised pool. In the latter case the pool could be unuseable for up to a week!!!!) On the website however, in the very same paragrpaph it also recommends the more traditional breakpoint dosage regimen of adding free chlorine to 10 times the combined chlorine reading. Which of these is correct- adding free chlorine to 10 times the combined chlorine reading (usually <1ppm so 10ppm of free chlorine would normally do it) or hitting the pool with 10 times the normal daily dose?
Edited by Mal T (07/31/10 09:47 AM)
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#3274 - 08/02/10 11:55 AM
Re: super-chlorination
[Re: Mal T]
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JessicaHarwell
Expert
Registered: 03/23/10
Posts: 73
(75.144.51.161)
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You can just use a shock treatment (which is between 50-75% available chlorine) to hyper chlorinate you pool.
Jessica Harwell
Pool Safety Covers
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#3279 - 08/07/10 01:36 AM
Re: super-chlorination
[Re: JessicaHarwell]
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rynadesouza
Newbie
Registered: 08/07/10
Posts: 2
(122.170.82.1)
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Very True, you do have to periodically shock pool or spa water. And true, it is often done with chlorin. Well According to me, Permonosulfates effectively control the formation of chloramines, which cause odours, reduce disinfection and cause eye and skin irritation.
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#3292 - 08/12/10 06:25 PM
Re: super-chlorination
[Re: Jeff Baxter]
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chem geek
Veteran
Registered: 06/19/08
Posts: 18
(192.68.228.4)
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Which of these is correct- adding free chlorine to 10 times the combined chlorine reading (usually <1ppm so 10ppm of free chlorine would normally do it) or hitting the pool with 10 times the normal daily dose?
Neither is correct. The 10x rule is incorrect since it came from chlorine oxidation of ammonia, but Combined Chlorine (CC) is in units of chlorine not ammonia so is a factor of 5 different. Also, CC already has chlorine attached to the ammonia so less chlorine is needed to achieve "breakpoint". Finally, if there is any measurable Free Chlorine (FC) at all in the water, then oxidation of ammonia, urea and other nitrogenous compounds is happening continuously. A higher FC level just makes it go faster, but there is no magic number needed to make it happen so long as you keep having some FC in the water.
The specifics are the following for the breakpoint chlorination rule:
3HOCl + 2NH3 ---> 2N2(g) + 3H2O + 3H+ + 3Cl-
Hypochlorous Acid + Ammonia ---> Nitrogen Gas + Water + Hydrogen Ion + Chloride Ion
So the molar ratio of chlorine to ammonia is 3:2 or 1.5 to 1. Chlorine is measured in ppm Cl2 units (molecular weight 70.906 g/mole) while ammonia is measured in ppm N units (molecular weight 14.0067 g/mole) so 1.5*70.906/14.0067 = 7.5935 and some more chlorine needed to get over the dichloramine hump this comes to 8-10 from which the simplified 10x rule came. CC is measured in chlorine units, not ammonia units, so instead of 10x it's really more like 2x, but there's also one chlorine already attached to monochloramine so it's really only 1x or the same amount of FC needed as CC.
If one does a similar analysis for urea, one still doesn't get more than 3x and again this is a stochiometric amount (plus getting over the "hump" of quadchlorourea) meaning how much total chlorine will be needed cumulatively, NOT how much has to be there to make the reaction at least start to occur.
All of this is a moot point anyway since in a properly maintained pool with a Free Chlorine (FC) at an appropriate level relative to the Cyanuric Acid (CYA) level, there is rarely any CC formed in the first place, at least in outdoor residential pools. See the Chlorine / CYA Chart.
You can just use a shock treatment (which is between 50-75% available chlorine) to hyper chlorinate you pool.
In a properly maintained pool with an appropriate FC/CYA ratio, one rarely needs to shock / superchlorinate a pool. By the way, there is no such thing as chlorine "shock" as a noun -- shock is a verb as in something you do in spite of the manufacturers labeling some standard chlorine products as "shock". It's identical chlorine. The 50-75% you refer to is Cal-Hypo and is identical whether it's called Cal-Hypo as a regular source of chlorine or Cal-Hypo for "shock". Trichlor is 90% available chlorine and comes in powdered form for "shock" (normally it comes in compressed slow-dissolving pucks) while Dichlor is usually around 55% available chlorine. However, these all have side effects as follows:
For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by at least 7 ppm.
The best chlorine to use without these CYA and CH side effects is chlorinating liquid or bleach and can be used for regular chlorination as well as for any rare "shocking".
Very True, you do have to periodically shock pool or spa water. And true, it is often done with chlorin. Well According to me, Permonosulfates effectively control the formation of chloramines, which cause odours, reduce disinfection and cause eye and skin irritation.
In a properly maintained pool with an appropriate FC/CYA ratio, one rarely needs to shock / superchlorinate a pool.
i think the "10 times amount" you are referring to has to do with clearing up a green, or swampy pool. also, some people prefer to put the liquid shock in the pool weekly. like 1 or 2 gallons.
:
also remeber that most all shock is not stabilized (with cyanuric acid), like chlorine tabs are. so most "shocking products" do disspate (sp?) from the pool water rather rapidly.
Again, in a properly maintained pool with an appropriate FC/CYA ratio, one rarely needs to shock the pool.
Adding unstabilized chlorine to water that already has CYA in it will NOT result in the chlorine dissipating quickly. The chlorine will bind to CYA and also be shielded by it almost immediately. In the water, there will be no difference no matter the source of chlorine. The only differences in chlorine are in whatever else they add to the water (such as CYA from Trichlor and Dichlor and CH from Cal-Hypo) and in their effects on pH.
Richard
Edited by chem geek (08/12/10 06:34 PM)
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#3301 - 08/16/10 01:50 AM
Re: super-chlorination
[Re: chem geek]
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Mal T
Newbie
Registered: 07/31/10
Posts: 2
(121.209.32.46)
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chem geek,
Thank you for your comprehensive response. I thought I knew a bit about the topic but clearly there is so much more to understand!
If I understand you correctly you are saying that in a properly maintained pool the need to super-chlorine a pool should be rare. Secondly, if you do need to super-chlorinate a pool the conventional wisdom that you need to add free chlorine at a rate of 10 times the combined chlorine level measured in the pool is outdated and the actual level is much lower - this gels with what I read on the taylors technologies web site.
However, my original concern stemmed from the fact that a colleague was recommending 10 times the normal daily chlorine dose which I worked out to be the equivalent of 50ppm of free chlorine. I am presuming therefore that you would be saying that it would be rare that you would need to add even 5-10pmm of free chlorine, let alone 50ppm.
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#3315 - 08/22/10 12:41 AM
Re: super-chlorination
[Re: Mal T]
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chem geek
Veteran
Registered: 06/19/08
Posts: 18
(98.248.184.97)
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Yes, you are mostly correct. However, the Taylor website doesn't say anything about not having any need for weekly shocking. They do talk about some recent research on not needing the shock level to be so high, but that only accounts for the 1 of 1.5 chlorine already in Combined Chlorine and still ignores the factor of 5 error due to using the wrong units of measure (i.e. using ammonia units when chlorine units should be used).
In outdoor residential pools, maintaining the proper FC/CYA ratio will not only be sanitary, but will prevent algae growth and not require weekly shocking. Bather waste will be continually oxidized. It is only in higher bather load situations such as in many commercial/public pools where supplemental oxidation such as from ozone, UV, MPS or enzymes is needed to help breakdown the ammonia, urea and other organics from sweat, urine, dead skin, etc. faster. This is especially true in indoor pools since there is no UV from sunlight to assist in such oxidation (either through direct interaction with chloramines or via creation of free radicals from breakdown of chlorine). So even in such high bather load pools, weekly shocking shouldn't be needed if supplemental oxidation is used. The key is to keep up with the bather load -- using chlorine alone simply won't do that in a higher bather load pool and results in higher levels of disinfection by-products (DBPs).
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#3341 - 09/02/10 08:09 AM
Re: super-chlorination
[Re: chem geek]
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footie
Enthusiast
Registered: 08/31/10
Posts: 6
(88.96.34.177)
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I have always been told to only hyper-chlorinate family pool once or maybe twice a year. During which times I leave it for approximately a week and then reduce the levels of chlorine with sodium thiosulfate after which point it's fine to use.
This process usually raises the chlorine level to about 10ppm so I don't understand how you should ever need to raise this to 5 times that level?
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#3361 - 09/10/10 11:33 PM
Re: super-chlorination
[Re: footie]
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chem geek
Veteran
Registered: 06/19/08
Posts: 18
(98.248.184.97)
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The superchlorination rule that is wrong is the one that says to shock your pool to 10x the CC level. They don't say to shock it to 10x (or 5x) the normal FC level. I was referring to the incorrect 10x rule, not to just raising the FC to 10 ppm.
A properly managed outdoor residential pool should not need to be shocked regularly. If you are maintaining an FC level appropriate to the CYA level (see the Chlorine / CYA Chart in the Pool School) then oxidation of bather waste and killing of pathogens and prevention of algae are occurring continuously.
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