High Chlorine Demand
In the event the chlorine demand is beyond the capability of the chlorine generator, then a
longer run time or occasional manual top-up dose with liquid chlorine may be all that is
required.
During periods of hot weather and high pool usage you should expect that the demand on
chlorine will be much higher than usual. Keep an eye on the free chlorine level, and have
some liquid chlorine available to use if the free chlorine level drops below 1.0ppm.
In addition to hot weather and high bather load, there are a few other common reasons
why chlorine demand might be higher than usual, these are:
1. Organic Debris – such as leaves, etc. in the water.
2. Low stabilizer level (applies to outdoor pools only).
3. High 'combined chlorine' level (explained on next page).
Chlorine Stabilizer – Cyanuric Acid
For outdoor pools Pool Lab highly recommends using stabilizer (Cyanuric Acid) at a
concentration of between 50 – 80ppm. An outdoor pool exposed to sunlight will have
extremely high chlorine demand without sufficient stabilizer in the water. Never exceed
100ppm concentration of cyanuric acid, as this will prevent the chlorine from sanitizing the
water efficiently.
Combined Chlorine - Chloramines
A common cause for unusually high chlorine demand is the presence of chloramines in the
pool water, detectable when a Total Chlorine test result is higher than a Free Chlorine test
result by greater than 1.0ppm. The difference between these two test results is known as
the “Combined Chlorine”. More advanced test kits will include the Total Chlorine test,
otherwise you will need to have your water tested professionally to check for this.
Chloramines are formed when free chlorine reacts with ammonia like compounds called
'amines', and this will build up over time. Chloramines are a poor disinfectant and also
reduce the disinfecting power of the free chlorine in the water. Chloramines are irritating
to the eyes and respitory system, and are responsible for the “chlorine smell” most
noticeable around heavily used indoor pools.
As a general rule Pool Lab recommend shock dosing your pool with liquid chlorine at least
once every swim season as this can significantly reduce chlorine demand and greatly
improves the disinfecting power of the free chlorine in the water. For pools with heavier
bather loads this may need to be done more often.
An accurate measurement of the pool volume and combined chlorine level is essential for
calculating the required amount of chlorine to perform the shock dose.
You should consult your local swimming pool professionals for advice on this
procedure, and how often is appropriate for your pool.
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