iQntrol DOS-MODBUS
Original manual in German Version 1.0.2 2022.10.06
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3
Important facts about swimming pool water properties
3.1
Auxiliary hygiene parameters
The following information is meant to offer a preliminary overview about the most important auxiliary hygiene parameters in the
treatment of swimming pool water. Further information is available from your swimming pool dealer, the chemicals supplier, or
the book trade. The information provided here refers to DIN 19643 for swimming pool water in public pools.
Devices that are installed outside of Germany should comply wit the county-specific regulations and statutes, e.g., ÖNORM, etc.
3.1.1
pH value
The pH value has a decisive effect on the chemicals added to the swimming pool cycle. If the pH value is too high, it negatively
affects the germ-killing speed of disinfectants containing chlorine. The likelihood of lime precipitation and water clouding
increases. If the pH value drops too low for an extended time, there is a risk that the treatment system and the basin may be
damaged.
According to the DIN, a pH value around pH7 should be aimed for.
Values below pH6.5 and above pH7.6 should be avoided.
3.1.2
Redox voltage
The redox voltage indicates the ratio between reducing substances (organic contaminations) and oxidising power (active chlorine
content) in the pool water. The redox voltage serves as a measure for assessing the hygienic basin water quality. The higher the
redox voltage, the faster germs and bacteria will be killed. To achieve a sufficiently fast germicidal effect, the redox voltage in
private pools should also comply with the values specified by the DIN. In this context, the amount of free chlorine measured with
the DPD1 method should be between 0.3 and 0.6 mg/l.
The chlorine's disinfecting power essentially depends on the basin water’s pH value. The higher the pH value, the lower the
disinfecting power; if the pH value decreases, the disinfecting power increases at a constant chlorine level.
If the redox voltage is far below 700 mV at a free chlorine content between 0.3 and 0.6 mg/l, the complete function of the
swimming pool water treatment must be checked.
According to the standard a redox voltage around 750 mV should be aimed for.
Values below 650 and above 800 mV should be avoided.
3.1.3
free chlorine
The chlorine available for disinfection in the pool water is called free chlorine. Free chlorine is detected by means of the DPD1
method.
According to the DIN, the free chlorine content should be kept between 0.3 and 1.5 mg/l.
Values below 0.2 and above 1.2 mg/l should be avoided.
3.1.4
combined chlorine
Combined chlorine is the product of a reaction between organic contamination introduced in the pool and a chlorine-containing
disinfectant. Combined chlorine causes the characteristic indoor pool smell and may lead to skin irritation and red eyes.
Ideally, the organic chlorine compounds will be retained in the swimming pool filter system and flushed out via the regular
backwashing. If the filter system does not work correctly, or if the backwashing is not conducted in a proper fashion, combined
chlorine may accumulate in the swimming pool cycle. If the water starts smelling of chlorine, it is high time to conduct a chlorine
measurement by means of the DPD3 measuring.
The concentration of combined chlorine results from the difference between the overall chlorine content and the amount of free
chlorine in the water. Observe the instructions of the analytic device's manufacturer when determining the concentration.
Combined chlorine can only be reduced by dilution, i.e., with vigorous backwashing or by a shock chlorination, if applicable.
Consult your swimming pool dealer.
According to the DIN, a combined chlorine content below 0.2 mg/l should be aimed for.
“Chlorine odours” can result above a combined chlorine content of approx. 0.3 to 0.4 mg/l. (characteristic indoor pool smell)
3.1.5
Cyanuric acid
Cyanuric acid is found in organic chlorine products (stabilized chlorine). If disinfection is carried out with organic chlorine, cyanuric
acid will accumulate. Cyanuric acid can only be reduced by dilution, i.e. with vigorous backwashing. Ask your swimming pool
retailer.
According to the standard, a maximum concentration of 100 mg/l must be observed.
Tip
Since the pH value is an elementary factor in the swimming pool treatment, the dosing of chlorine-containing
disinfectants is only released once the pH value has entered the control range!