One of the most common causes of pool water problems in heated swimming pools is the presence of chloramines. Chloramines, also referred to as combined-chlorines, are molecules formed by the combination of chlorine in the form of Hypochlorous Acid (HOCl) and organic wastes (saliva, perspiration, urine) in the form nitrogen or ammonia. Chloramines produce the chlorine odour that many people do not like (tear gas is a form of Chloramines).
When people complain of too much chlorine, it is almost always a case of combined chlorine or chloramines as opposed to a proper level of Free Available Chlorine (FAC) that creates the odour. The misconception is that the pool smells of chlorine, therefore (in the pool owners mind) they have too much chlorine present in the pool. At this point they usually stop adding anything to the pool, effectively ignoring the problem. Pool owners are seldom convinced that their true problem is a lack of chlorine and in particular FAC.
Chloramines are the root cause 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 oxidation, more chloramines are formed thereby exacerbating the problem leading to obvious problems such as cloudy water or algae growth. Pool owners (and sometimes pool schools) unfamiliar with chloramines and chlorine demand, often try to treat the symptoms (cloudy water or algae) rather than dealing with the root cause. Without this awareness of chloramines & chlorine demand, pool owners may never receive the help they need.
Chloramines (combined chlorine) are poor sanitisers. The presence of chloramines (and dichloramines/ trichloramines) causes the following physical symptoms:
- red, burning eyes;
- burning sensation in nose, throat and lungs;
- dry, itchy skin and dry hair;
- Breathing difficulty, particularly in young children.
- A strong odour of chlorine around the pool
Furthermore, the pool has a tendency to become cloudy or green due to the low sanitising ability of the combined chlorine (chloramines).
When chlorine is added to water, some of it is soon consumed by destroying algae, bacteria and other oxidisible material in the water. The amount of chlorine so consumed is referred to as the chlorine demand of the water. Only once the chlorine demand is satisfied, can any additional chlorine added be tested as a chlorine residual. Two types of chlorine residual can exist: 1. Free available chlorine residual - this is the chlorine available to do its job of sanitising the water. 2. Combined chlorine residual - this is chlorine combined with simple nitrogen compounds such as ammonia and urea. This chlorine (or more correctly chloramines) is not as nearly as effective as free available chlorine.
It's essential to maintain a free available chlorine (FAC) residual at all times, to achieve sparkling clear, hygienic pool water. This is accomplished by regular shock treatment. Shock treatment (super chlorination) consists of simply adding a larger than normal dose of chlorine to burn out nitrogenous waste. When chloramines are removed by a shock treatment, better efficiency of chlorine is achieved. More of the chlorine residual can then exist as the free or active form, rather than as the less effective combined form.
Testing for chlorine in pool water
All good chlorine test kits and pool test strips allow you to determine free chlorine as well as total chlorine. Combined chlorine is calculated from these values as follows:
Combined chlorine = total chlorine - free chlorine
The combined chlorine value should ideally be as close to zero as possible. Some cheaper test kits use liquid reagents (drops. If the reagent bottle is marked "OTO" then you should consider a better test kit. OTO (orthotolodine) using a yellow colour chart, will show only Total Chlorine, not differentiating the difference between FAC and chloramines present. Chlorine testing using the more accurate DPD tests, using a pink colour chart, provides separate tests for Free Chlorine as well as Total Chlorine and is therefore preferable.
Destroying combined chlorine compounds
The appropriate amount of chlorine needed to reach breakpoint oxidation usually recognized as 10 ppm FAC (free available chlorine) to correct each 1.0 ppm of combined chlorine. Failing to reach this level actually contributes to the chlorine demand problem as more chloramines are formed. Your pool professional may advise you to put in a larger than normal dose of shock treatment in your cloudy pool. When chloramines exist, this is necessary in order to reach breakpoint oxidation. Breakpoint oxidation is simply a level of 10 or more times of chlorine compared to that of the combined chlorine level. That means potentially adding large amounts of shock at one time! Yes, at one time!
Reaching breakpoint chlorination is an "all or nothing" action. Think of it as trying to jump across a divide; you can't come close. You must reach the other side. You can't almost make it. Whether you're 5 centimetres short or 50 metres short, you still did not make it, and along with it comes the fall.
This is why we constantly remind consumers of the need to shock treat their pools. Weekly shocking during the summer months when the pool is in use will greatly reduce the potential of chlorine demand and may potentially even reduce chlorine consumption in the long run.