Chlorine Demand (Sanitizer or Oxidizer)

Understanding a difficult problem...

Chlorine Demand is a pool water chemistry topic that is getting more attention due to changing climates, consumer's water chemistry and understanding of the problem.  It is also becoming a greater issue in many private & commercial pools.

Chlorine Demand is defined as "the quantity of chlorine reduced or converted to inert or less active forms of chlorine by substances in the water." Faust and Aly's Chemistry of Water Treatment further state that, "since  chlorine is a non-selective oxidant, almost any substance in the water...will  react and consume chlorine."  


In other words, the more "stuff"  dissolved in the pool water, whether organic or inorganic; chemical, vegetable  or mineral; heavy, constant rainfall can cause a chlorine demand.  Or more simply  stated, not being able to successfully maintain a chlorine residual following a  shock treatment. Certain household  cleaners that are not specifically formulated for in-pool-water use will add  components such as phosphates or nitrates will interfere with the pool's  sanitizer causing a chlorine demand

A couple of the most common causes for chlorine demand that we see are in the spring at pool opening time.  Pools are left idle & unattended for months at end without treatment.  The problem is  worsened if the pool had been closed the prior season without being thoroughly  cleaned - accumulations of leaves, debris, dirt, etc. are left to sit in the  pool for the winter. Leaves & debris will break down & add nitrogen along with other organic contaminants leading to a chlorine demand issue.  I can personally attest that a clean & properly closed pool will open in the spring  almost worry free.

Another  cause that may prove suspect, at least in our line of thinking, is the Chloramine issue.  As you  remember, chloramines are chlorine molecules that are chemically linked up (we  call them contaminated) with organic waste such as nitrogen, ammonia, etc.   More & more local water treatment authorities are using chloramines to  sanitize the  drinking water supply these days.  Chloramines are pretty effective in killing pathogens in the drinking water supply.  However, chloramines are not effective oxidizers.  

You've probably noticed a regular pink line in your  home sink, shower or toilet bowl, especially over the past 4 to 5 years.  Those spots need more regular cleaning.  That's the same pink slime that is  in your swimming pool!  Chloramines are used because they are pretty  effective and less "offensive" to those who want to rid our planet of chlorine.   That premise is utter foolishness since you can't ban or get rid of an element!   Anyway, as you top off your pool with the garden hose, you're putting more  chloramines into your pool every time and aggravating an already serious  problem.  Please keep in mind that this issue is NOT pertinent to folks  with well water (you have your own issues). Click here for further information on chloramines.

Since 1992, BioGuard's Technical Services Department has gathered a huge amount of data concerning chlorine demand.  It appears that the situation has become more widespread each year.  Here are some actions that can help in dealing with Chlorine Demand.

  1. Doing a proper Chlorine Demand Test.  Your local BioGuard®  Platinum Dealer should have a Chlorine Demand test station.  When     determining the ACTUAL Chlorine Demand, it is imperative that the solution & corrective action be accurate. 

    Liken it to jumping across the     Grand Canyon, if you miss, you miss!  If it takes 20 lbs of Shock to break the chlorine demand, using 19 lbs will make the problem worse; 20 lbs or more of Shock will treat the issue.
  2. Maintenance of an adequate     sanitizer being added to the swimming pool on a daily basis. Be sure to have the correct number of chlorine sticks or tablets dissolving into the pool.  Check this as often as daily by visually examining the chlorine to see that it is eroding (whether in the skimmer or in a chlorinator) at a "normal" rate.  Normal refers to what you have "normally" experienced in the past.  Cool water, slower erosion/dissolution rate; warmer water, faster erosion/dissolution rate.
  3. The Pool MUST BE SHOCKED EVERY WEEK. PERIOD.  Shocking oxidizes much of the "stuff" that was mentioned earlier.  Download a FREE brochure to learn about shocking.
  4. If you are using a solar blanket, REMOVE IT!  After ANY chemical addition, the chemical reaction must have time to GAS-OFF in order to achieve the proper results.

Although a singular cause for Chlorine Demand has not been determined (there are many), we have found a common thread in many of these cases.  One common thread is if a pool is kept closed longer in the spring (covered without a sanitizer).  Heavy rainfall that has ammonia present will cause a Chlorine Demand.  Accidental addition of household fertilizers or any compound that can be oxidized by chlorine will result in a Chlorine Demand.

In conclusion, Chlorine Demand needs our attention.  Only careful monitoring and quick treatment may be successful for a clear pool.   BIOGUARD PLATINUM DEALER are the only dealers who hve this technology.

Par Pool & Spa can perform a  Chlorine Demand test for you. If you don't have a local  BioGuard Dealer with a Chlorine Demand Test Station, you may OVERNIGHT a  sample to us for testing & analysis.  We will perform a complete BioGuard Test using AccuScan and the AccuDemand 30 test stations and will provide you  with BioGuard Alex results as well as some of our own recommendations.   Please fill out this form (new window will open), print it, and include it with your ONE QUART water sample (must be sent in a clean, plastic bottle that was NOT used to hold  cleaning fluids, soda, food in general - an empty water bottle is best). Please  note that there is a $25.00 charge for this testing & analysis service.  We will  contact you by telephone with the results & recommendations.  

EVERYTHING that is in water can contribute to a Chlorine Demand.
EVERYTHING that is in water can contribute to a Chlorine Demand.

Understanding Chloramines

Your pool shouldn't smell like a chlorine bath...

One of the most common causes of water related problems in swimming pools is the presence of chloramines. Chloramines are often referred to as "combined-chlorines" because they are molecules formed by the combination of chlorine in the form of Hypochlorous Acid (HOCl) and organic wastes (such as saliva, perspiration, urine) in the form nitrogen or ammonia. Chloramines produce the "chlorine odor" that many people do not like (tear gas is a form of Chloramine).  

When people complain of "too much" chlorine, it is almost always the case of combined chlorine or chloramines causing the foul odor as opposed to a proper level of Free Available Chlorine (FAC). 

But foul chlorine odors are just the ugly mask of the underlying problems present in swimming pool water, sometimes caused by the improper addition of too many pool chemicals. Chloramines are the root of many problems in pool water. Chloramines cause problems because of their stability and persistence.  This stability and persistence forms additional Chloramines. This is chlorine demand (consumption) at its finest.  (Consumers complain that they "just shocked" the pool but  there's no chlorine showing when tested.) As more chlorine is added without reaching breakpoint, more chloramines are formed thereby exacerbating the problem leading to what I'll call "obvious problems" such as cloudy water or algae growth.  

Homeowners and/or  pool dealers unfamiliar with chloramines and chlorine demand begin treating the symptoms (cloudy water or algae) rather than dealing with the root cause especially after the second or third treatment.  Without the knowledge of chloramines & chlorine demand, consumers  may not receive the help they need. 

Basic water testing & water chemistry, as mentioned in Key 4 and Key 5 of the 5 Keys to Pool Care, is "key" to preventing chloramines. 

Chlorine demand testing stations aid greatly in determining the appropriate amount of chlorine needed to  reach breakpoint chlorination usually recognized as 10 ppm FAC  (free available chlorine) to correct each  1.0 ppm of combined chlorine. Failing to realize this amount actually contributes to the chlorine demand problem as more chloramines are formed.  We often hear the  consumer complain that "my pool guy told me to put in a double dose of shock to treat my cloudy pool."  That amount may indeed fall VERY  short of the actual need.  When a chlorine demand test is performed, it is often necessary that a dose of 10, 20 or more times of chlorine shock is needed to reach breakpoint chlorination. That means potentially  adding 40, 50 or more pounds of shock (in the form of cal hypo) at one time! 

Yes, at one time!  If you try spreading it out (even over a few  hours) you've defeated the cure and unwittingly added to the problem.

We describe the problem this way to our customers in regards to reaching  breakpoint or satisfying chlorine demand:  Reaching breakpoint chlorination is an all or nothing proposition. Think of it as trying to jump the Grand Canyon in a single  bound; you can't "come close".  You MUST reach the other side FIRMLY.  You can't  "almost make it."  Whether you're 2 inches short or 100 feet short, you're still  short. 

This is where our constant reminding of consumers of the need to weekly shock their chlorine or bromine pool.  Weekly shocking during the entire time the pool is open & operating will greatly reduce the potential of chlorine demand or  consumption. 

PoolSpaGuru has been using a state of the art Chlorine Demand test station, BioGuard's Accu-Demand 30. An exact demand is figured out in about 30 minutes & is virtually 100% accurate.  The old method took 24 hours & was not as accurate.  This gets the problem rectified immediately, as opposed to  waiting an additional day or 2 when the results would be ready and more chloramines form.  

The Accu-Demand 30 will be the best available method to accurately perform a Chlorine Demand test on the market.  If you are one of our  out of town customers, you can send a water sample for testing.  There will be  a small fee for this service; however we will call you with the results and recommendations within 24 hours of our receipt of the sample. 

Another facet to the chlorine demand and chloramines problem is the misconception that the pool "smells of chlorine" therefore (in the novice's mind) I've got too much chlorine or too many chemicals present in the water, and they stop adding anything to the pool, effectively ignoring the problem. Testing goes out the window; pH and overall water balance go out of balance.  The pool owner is not  convinced that their true problem is a lack of chlorine and particularly FAC.   

This is especially true if the homeowner or pool operator is using OTO  (orthotolodine will produce results for Total Chlorine only, using yellow color standards, not differentiating the difference between FAC and chloramines  present) for chlorine testing as opposed to the more accurate DPD (using pink  color standards) method (uses separate tests for Free Chlorine as well as Total  Chlorine).


Controlling small amounts (under 2.0 ppm) of chloramines is relatively easy.  Shock the pool with a good-quality granular chlorine or use an oxidizing compound containing  potassium mono-persulfate.  Mono-persulfate shocks are great because they don't add additional chlorine that may contribute to  further Chloramine formation.  We have found that even when there are  larger amounts of chloramines present, the mono-persulfate works well in reducing the chloramines by oxidizing these wastes and releasing the combined chlorines.  Breakpoint chlorination often-times becomes simpler to achieve.  Again, weekly shocking of the pool is the preferred preventative procedure. 

Just because the pool water looks good doesn't mean that everything is balanced and working properly. 

A lurking problem? Another potential area or source  of the Chloramine problem may be something we as dealers or homeowners  have no control over.  The following comments and questions are purely speculative and have not been scientifically proved.  The premises are  based on over 30 years of experiential observation and hopefully common sense.  The Chloramine problems that we've been discussing in this article have become more prevalent each passing swimming season over the past 2 decades.  There's a greater frequency and severity of the  Chloramine issue. 

In the early and mid 1990's, the nation's public drinking water suppliers began switching to using chloramines in the water sanitizing process; known as "chloramination".  Chloramines were and are known to be more stable and persistent  as we've already mentioned.  Chloramines do a good job controlling normal bacteria and "stuff" in water. I will not discuss the reasons why chloramines are the preferred and even mandated form of bacteria control in potable water systems.  That is a discussion for the  scientist and politician.  We are instead looking at daily observations.   

Throughout the 1990's we heard  the cry of "get of rid of chlorine".  Chlorine was given a bad rap.  Mainly from people who don't know what they're talking about.  After all, how do you ban an element?  People didn't like the so-called taste of chlorine in their drinking water. Given a choice of dangerous coli-form bacteria or a slight chlorine taste, I'll take the chlorine taste. 

Chlorine has undoubtedly saved thousands, and I dare say millions, of lives around the world in purifying water.  We see what untreated water looks & smells like and its devastating effects.  This is especially poignant in the wake of Hurricanes Katrina, Rita, Maria and others.


These are observations over the past  10 - 15 years regarding swimming pools: Increasing frequency and severity in treating chloramines in swimming pool water; increased  questions of chlorine demand or consumption; more frequent consumer complaints of skin rashes or eye irritation when using a pool, spa or  hot tub. In the late 1980's and early 1990's, pink slime and 'white water mold' were being blamed on biguanide usage, until it  was noticed that there was this pink stuff coming from the garden hose.  

From a potable drinking water standpoint these are our observations.  Tap water rarely smells of chlorine. People notice the need to more frequently clean a bathroom or sink areas.  The toilet always seems to have a ring.  Often times when  the garden hose is turned on, a glob of icky, pink stuff comes out.  What's going on? 


Now we tell our pool or spa  customers to run the water for a minute or two to flush out the garden  hose before adding that water to the pool, spa or hot tub (now we're  wasting water, a very valuable resource).  We don't want the biofilm in the pool or spa, but what about the chloramines coming  in? Do we have a potential situation where pathogens, that may be  present in the drinking water, are being killed but then their  waste is not being oxidized (utilizing chlorine has some oxidizing  attributes, chloramines do not)? Why is there a build-up of bio-films  in garden hoses, sinks, toilets, piping? 

Are chloramines good oxidizers? No. As pool & spa professionals, we know the necessity and  advantage that regular oxidation performs; we more fully get rid of ALL  of the stuff that is a potential contaminant.  This hypothesis is based  on the fact that if you add more chloramines to pool or spa water, you  will form even more unwanted chloramines.  It's a vicious  circle. Let's use this analogy:  I have a pile of garbage. By putting  some kind of chemical on the pile to kill the germs, I may have treated  it;  but the pile of garbage is still there.  Now if I then burn that  pile of garbage (oxidizing it), I've reduced it to a more  'harmless' ash, which by the way has a much smaller volume.  Does  this make sense?  Thatï's why shock treatments are often referred to as  oxidizers.  I suppose that's why BioGuard® named their shock  treatment Burn Out®.

The pool, spa and hot tub owner and user must understand these facts and act accordingly to protect not  only his or her investment, but also the health of the users. ...