10
Water maintenance
User Manual PoolManager
®
27
10.2.2
Redox value
(Disinfection with chlorine and bromine)
INFO
This section applies for the models PoolManager
®
Cl
and PoolManager
®
Br only.
The redox value of the pool water represents electric potential that can
be measured using a corresponding electrode (redox electrode).
It is the measurement of the water's oxidation potential, and therefore
of current disinfection effectiveness.
The redox value is a sum parameter that can be influenced by
numerous substances in the pool water.
Oxidizing substances (disinfectants) raise the redox value
•
Hypochlorous acid HOCl for disinfection with active chlorine
•
Hypobromous acid HOBr for disinfection with active bromine
Reducing substances (contaminants) lower the redox value
•
Inorganic and organic contaminants
•
Chloramine, oils, carbamide, sweat, germs, bacteria, algae,
leaves,etc.
Due to these numerous influences, it is generally not possible to
determine the chlorine/bromine level in the pool directly from the redox
value measured. It is, however, possible to set the desired
chlorine/bromine value in the pool and then to calculate the associated
redox value.
IMPORTANT NOTICE!
Determining the correct redox value
Widely different redox values can be yielded by various
pool types with the same chlorine value or bromine
value. For example, a chlorine value of 0.8 mg/l can
lead to a redox value of 720 mV in one pool, while in
another pool, it can lead to a redox value of 780 mV.
•
Do not rely on values seen in the past. Rather,
calculate the correct redox value for each individual
pool separately.
The redox value yielded for the desired chlorine/bromine value is
configured as a setpoint in PoolManager
®
. The control system ensures
that the redox value remains consistently on level with the configured
value.
As long as there are no significant changes in other influential
variables, the consistent redox value simultaneously provides for a
constant chlorine/bromine level in the pool, thereby ensuring reliable
disinfection.
10.2.3
Correlation pH value and disinfection
INFO
This section applies for the models PoolManager
®
Cl
and PoolManager
®
Br only.
The basic prerequisite for reliable and stable disinfection with chlorine
and bromine is a consistent and optimally configured pH value in the
pool.
There are two significant grounds for this:
For high pH values over 7.5, the portion of free chlorine present as
hypochlorous acid (HOCL) sinks dramatically. Since, however, only
hypochlorous acid is effective for disinfection, disinfection
effectiveness reduces in the same dimension. Sufficient disinfection is
no longer ensured.
Free chlorine measurement and the redox signal measured are not
directly dependent upon the level of free chlorine, but rather influenced
only by the hypochlorous acid, which influences disinfection. If,
however, the portion of hypochlorous acid changes due to a
fluctuating pH value, then that will necessarily lead to a fluctuating
redox value. Stable and reliable disinfection is then no longer possible.
The so-called dissociation curve shows the correlation between pH
value and the share of hypochlorous acid HOCl among all free
chlorine. At a pH of 6.5, ca. 95% of the free chlorine is present as
HOCl. At a pH of, however, that number is only 30%.
If control measurements are performed using the DPD method, then it
is important to know that the DPD measurement is always performed
at a pH value of ca. 6.2. That value is attained with an integrated pH
buffer in the DPD reagents. Thus, a DPD measurement measures all
free chlorine independently of the actual pH value in the pool.
HAZARD!
Overdosage if pH value is wrong
If disinfection is launched before the pH value is stably
in the ideal range of 7.0 to 7.5, then it may lead to
heavy overdosage of chlorine or bromine.
Potential consequence: Death or the gravest
degree of injury, heavy material damage.
•
Do not start disinfection with chlorine or bromine
until the pH value is stably in the ideal range
between 7.0 and 7.5.