Is chlorine demand real??.

[Pool_Fool]

Just curious to get ya'lls thoughts on this.
Pease share.... Is it real or just something the pool stores
Came up with to part us from our money?
And if you know it's real, then what causes it?

Thanks guys.
PF

 

[jblizzle]

I am not sure what "chlorine demand" is, but I assume it is a buzz word that the pool store uses as a catch all when they are not sure of what is going on in your water.

For example, most pool stores do not seem to understand the CYA/chlorine relationship. When they say a FC of 5 is fine, but your CYA is 100+ and your pool turns green ... well it must be chlorine demand when in fact you just have not had enough chlorine in the pool to compensate for the buffering capacity of the CYA.

On the other had, "chlorine demand" could just refer to the amount of FC consumed by a pool on a daily basis, due to sun exposure and organic consumption. This amount will very greatly as bather load and weather change.

I am curious to hear other thoughts on this as i am not 100% sure what the term is used to refer to.

 

[gkruske]

I heard that all the time before I bought the TF-100. And I understood chlorine demand to be a lot of things.

1. What blizzle said above about high CYA and low FC.
2. High combined chlorine, therefore the need to shock.

BUT....I think this term is more geared to the folks who are still using tablet feeders. So it was written in the cornerstones of Pool School, it's much easier to shock/chlorinate with bleach as opposed to tablets.

 

[duraleigh]

I have always assumed it meant the amount of chlorine required to maintain your pool. On a typical summer day in a properly maintained pool, the "chlorine demand" will be somewhere around 2-3ppm in a 24 hour period.

If you allow that same pool to start growing algae (let the chlorine get too low), the presence of algae in your pool will increase the "chlorine demand" and you will start to consume ppm far in excess of 2-3ppm....thereby increasing the "demand".

Pool stores seem to often use those words as some sort of "test" that they can tell how much additional chlorine you need and, of course, there is no test for that.

BBBr's understand the consumptive nature of FC and it's relationship to CYA and it's impact upon algae. Adding all those up, we know through accurate testing, that we can monitor our pools health and can maintain that pool so the consumption of chlorine stays relatively consistent throughout the season.

 

[gkruske]

Fine explanation, Dave. When I was a neophyte to maintaining my pool, the pool store told me I had 'chlorine demand'. In the context of their ramblings, it was very low FC, and the inability to maintain FC. CC's might have been low too, but they always said I needed to shock the pool in order to get FC up.

No one ever mentioned CYA. Add a bag of this, add a bag of that, fill up the feeder with tabs and crank it up.

 

[Alex.t901]

Ok, so chlorine demand is a real thing, not something us pool guys just throw at you so you buy more chemicals. Basically, Chlorine demand is a "overload" on your sanitizing system. It is usually caused by any number of contaminates that oxidize faster than your regular dose of shock or chlorine feeders can keep up with.

Now, to treat it, you usually need to do a triple shock dose or more depending on the demand. only way to know exactly how much you will need is to go a dealer and have them run a chlorine demand test, which most should be able to do. In my experience i usually run into this issue when someone takes off for vacation for 2week or more and come back to find their pool VERY green.

This is what i do to treat it.

First, balance out the pool. this includes CYA, pH, Alkalinity etc. Afterwards i generally use a very high powered shock or a pure chlorine product. Super soluable, which is 99% sodium Dichlor, (1lb per 8000 gallons) from bioguard is my personal favorite. Take 2 3" Chlorine tablets per skimmer and break them up into smaller pieces to increase the rate at which they disolve and run the pump for 24 hours. And usually that gets rid of the issue. Sometimes a second dose may be required.

 

[zea3]

Ok, so chlorine demand is a real thing, not something us pool guys just throw at you so you buy more chemicals. Basically, Chlorine demand is a "overload" on your sanitizing system. It is usually caused by any number of contaminates that oxidize faster than your regular dose of shock or chlorine feeders can keep up with.

Now, to treat it, you usually need to do a triple shock dose or more depending on the demand. only way to know exactly how much you will need is to go a dealer and have them run a chlorine demand test, which most should be able to do. In my experience i usually run into this issue when someone takes off for vacation for 2week or more and come back to find their pool VERY green.

There is a direct correlation between the amount of contaminates in the water and the amount of chlorine needed to eliminate the contaminates and the CYA level of the pool. The higher the CYA level, the higher the chlorine will have to be to perform an effective shock process on the pool.
We recommend liquid chlorine as it will not add CYA or calcium to the water. The 2 main contributors to a green pool are too much CYA and/or not enough chlorine to meet the demand.

We recommend that pool owners buy a high quality FAS-DPD test kit, such as a Taylor K2006 or the TF 100 to test their pools. These kits will allow pool owners to test chlorine levels much higher than 5ppm, the usual maximum reading at the pool store. The ability to test higher chlorine levels allows pool owners to conduct the shock process effectively without having to guess the correct shock level.

This is what i do to treat it.

First, balance out the pool. this includes CYA, pH, Alkalinity etc. Afterwards i generally use a very high powered shock or a pure chlorine product. Super soluable, which is 99% sodium Dichlor, (1lb per 8000 gallons) from bioguard is my personal favorite. Take 2 3" Chlorine tablets per skimmer and break them up into smaller pieces to increase the rate at which they disolve and run the pump for 24 hours. And usually that gets rid of the issue. Sometimes a second dose may be required.

We don't recommend adding chlorine without testing the levels during the process. Dissolving tablets in the skimmer needs to be carefully monitored to prevent damage to the pump and skimmer. Read through pool school, especially the defeating algae chapter and the turning your swamp into a sparkling oasis chapter for more information on the shock process.

 

[anonapersona]

. only way to know exactly how much you will need is to go a dealer and have them run a chlorine demand test, which most should be able to do.

So, I ought to be able to call up a dealer and have them explain what this test consists of?


I called one of my local pool stores (the better of the bunch) to ask "What is a chlorine demand test?" I had to stress that this is a philosophical question, for they were asking what numbers I had. I asked again, "If someone runs a Chlorine Demand test, what do they do?"

"They just test the chlorine level"

I said, "Like, the chlorine is 2.0?"

"Yes, that tells you how much chlorine you will need to add" Presumably to get to some stated level.

Sounds pretty bogus to me.

Edit-- I called another pool store and asked again. The man there was stumped.... "I've never done a Chlorine Demand test".

 

[Swampwoman]

Well, whether or not the average pool store uses the term correctly or not, I believe technicians etc. are trained that the term refers to the inability to maintain a normal chlorine residual.

I don't think there's anything "made up" about the term itself -- we all know that chlorine consumption fluctuates according to water balance and nascent algae or contaminants, and that if for example you have high ammonia, you can add chlorine and not get a residual reading, and that usually, shocking will remedy this, and that sometimes, eg with ammonia, that could require a shock level 8 times the ammonia reading.

So sure, it's real, and it's something we all help people with everyday on this bb, which is not to say there arent retail employees out there who use the term incorrectly or have no true clue what it really means or who in fact pervert the phenom to sell product.

 

[anonapersona]

It appears that, from reading the posts here, there is no actual definition of "Chlorine Demand".

It refers to A) chlorine consumption on a daily basis, or B) excessive chlorine requirements due to excessive CYA levels, or C) the calculated amount of chlorine that will be needed over time to clear an ammonia problem.

Until there is some clarity as to what that term refers to, I will avoid using that except in situations where the meaning is defined. And when others use that term, we ought to get them to spell out what exactly they are referring to. As used commonly, it is just too vague.

 

[Swampwoman]

Here's a water tech definition:

Most water treatment plants are required to disinfect the water, a process used to kill harmful bacteria.  The most frequently used method of disinfection is the addition of chlorine.  Here, we will briefly introduce three terms used during chlorination - chlorine dose, chlorine demand, and chlorine residual.  These three characteristics are related to each other using the following equation:

(Chlorine demand) = (Chlorine dose) - (Chlorine residual)

The amount of chlorine added to the water is known as the chlorine dose.  This is a measured quantity chosen by the operator and introduced into the water using a chlorinator or hypochlorinator. 

As the chlorine reacts with bacteria and chemicals in the water, some of the chlorine is used up.  The amount of chlorine used up by reacting with substances in the water is known as the chlorine
demand.  If nothing reacts with the chlorine (as would be the case in distilled water), then the
chlorine demand is zero.  However, in most cases the operator should count on some of the
chlorine dose being used up when it reacts with substances in the water. 

The amount of chlorine remaining in the water after some of the chlorine reacts with substances in
the water is known as the chlorine residual.  This lab introduces a test which can be used to
calculate the chlorine residual.  The chlorine residual is the most important of these three values -
dose, demand, and residual - because it represents the actual amount of chlorine remaining in the
water to act as a disinfectant.

So it seems to me the mistake people are making is to qualify "chlorine demand" with a word like "high".

To me, the phrase seems natural -- I'd hate to see an accurate phrase be eschewed because of misuse in the pool store

 

[Swampwoman]

^meant to say FAILING to use qualifier/modifier such as "high". iPad is awkward for editing

 

[Pool_Fool]

So in reflection my local store charges an extra $45 to tell me the cc numbers

 

[Swampwoman]

That sounds about right for the low low price of $25 I'll tell ya your chlorine demand if you tell me your FC after dosing

 

[JasonLion]

Chlorine demand almost never applies to a swimming pool. The only remotely common pool situation where chlorine demand is at all useful is if you have ammonia in the water. The chlorine demand is then the amount of chlorine required to burn off all of the ammonia in the water. This is the same thing as Swampwoman's "water tech" definition. Of course, the actual amount of chlorine you will need to use could easily be more than the chlorine demand, as chlorine can be lost for other reasons (like sunlight).

Chlorine demand isn't a very useful concept unless you have ammonia in the water. Chlorine lost to sunlight doesn't count as chlorine demand, nor does chlorine lost to ongoing algae growth. While algae does have a nominal chlorine demand, the amount of chlorine that would be required to kill and break down all of the algae, that assumes that everything happens instantly, that there is no further algae growth and no chlorine lost to sunlight. So with algae the chlorine demand is going to wildly under estimate the amount of chlorine required and really isn't a useful number.

Because chlorine lost to sunlight and algae are the dominant uses of chlorine in a residential pool, neither of which is usefully reflected in chlorine demand, and because algae growth rates depend on chlorine levels, and not chlorine amounts, we use an approach based on target FC levels, rather than an approach based on chlorine demand. As it happens, the targeted levels approach works just fine even when you do have ammonia in the water, so there is hardly ever any reason to know, or try to figure out, your chlorine demand.

It is worth noting that the phrase "chlorine demand" often gets used for things that do not at all match the definition. The most common usage is by pool store people trying to explain high CYA levels and algae when they don't actually have any idea what is going on. Chlorine demand does occasionally get used correctly when dealing with ammonia, but that is rather less common.

 

[Stuamurr]

CIMSPA - The Chartered Institute for the Management of Sport and Physical Activity here in the UK lists Chlorine Demand in the NPPOC Operator's Certificate Training Manual (from memory as I don't have the folder to hand) as a figure for Free Chlorine which Pool Professionals should devise on their own based on regular checking and recording of Pool/Spa Water Quality, to establish how much Chlorine is required in the water you manage.

In simple terms it is merely a plant room operator figuring out how much Chlorine is going to be used up, not a test that can carried out etc, merely a guide to what you should have ready in day tanks etc, if you know for example under heavy bather loads etc you will be using around 5ppm FC that day, then that is your Chlorine Demand, there is nothing magical or technical about the term.

Chlorine Demand can be targeted into several categories, mainly:
Bather FC Loss
Sunlight FC Loss
Organics FC Loss

All these items as you are all aware contribute to the "Chlorine Demand" in a swimming pool. I think it sounds like some Pool Shops are trying to overcomplicate a simple phrase. Most of us already are aware of what the Chlorine Demand of our pool is, but have never associated it with the term.

>>EDIT: Reading Jason's post who posted at the same time as me, I agree Chlorine Demand is nothing that residential pool owners should need to nor have to worry about, it's usefull in public pools, to maintain pro-active chlorination during operating hours, given the constraints of operating FC residual's but that is all.

 

[Swampwoman]

Yes, actually, when I was testing my pool this am I noticed that Taylor in it's kit pamphlet also uses the word "demand" when referring to chlorine, acid and base required to get to desired residuals/levels. The pamphlet also refers to "chlorine breakpoint" to describe the amount of chlorine needed to destroy cc's -- which it cites as ten times the value. Eg. So if you have 2 ppm cc, it implied you need to dose to 20 ppm to "break" the cc (remove it/oxidize it/shock it). So that's likely where the mangled poolstore-speak originates.

There's usually a nugget of fact, albeit perverted fact, floating around somewhere when on is in the act of poolstoring Or should I say pool-storying

FWIW though, I won't blame the word demand -- seems like a fair use. Every day we figure out the "dose" we "need" (demand) to create a "residual" due to the chlorine typically "used" in a given period. That process, whether engaged in by a homeowner, a pool tech, or a water quality specialist is in essences, assessing chlorine demand, methinks.