Emec Centurio POOL, Operating Manual

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Dissociation of hypochlorous acid related to pH value
The pH represents an index of the acidity of a solution. From a chemical point of view, the pH indicates the base10 of the
concentration of H+ ions present in a solution and therefore the ability of the solution itself to accept OH- and neutralize
them. In practice, a low pH solution is ACID, while a high pH solution is BASIC. The pH value is expressed with a pure
number, without a unit of measurement.
The pH value of swimming pool water is very important to be monitored and controlled constantly. For example, the result
of a too high pH is to literally throw the chlorine that we put into the water, because it will have no effect. The reason is
given by the fact that the hypochlorous acid, i.e. the disinfectant substance that is released from all the chlorine-based
products introduced into the tank water, is not stable but tends to dissociate continuously according to the reaction:
HClO > H+ and ClO-
The dissociation of hypochlorous acid is strongly influenced by the pH value of the water, as shown in the graph below:
With a pH around 6 the dissociation in practice does not take place, while if it rises above the value of 7.5 surely at least
half of the hypochlorous acid present in the solution will dissociate. Since for an effective water disinfection it is important
that the molecule remains indissociated and the dissociation depends heavily on the pH value, so the need to keep the
pH under control becomes one of the fundamental aspects of the chemical conditioning of the pool.
Within the “TEMPERATURE / SETTINGS” menu, there is a submenu visible only if Chlorine probes* capable of
managing this function are connected to the controller, enable the “% Active Chlorine” item on “SHOW” to display the
percentage of Active Chlorine detected.
*SCL 1/2, SCL 1/5, SCL 1/20, SCL 1/200, SCL 1/2, ECL 6,7,12,20, ECL 6,7,12,20 BR, SCL 18/10, SCL 18/2, SCL 18/20
ACID
NEUTRAL
BASIC