3
c) pH
pH is a measure of the concentration of hydrogen ions in a solution, or in simpler terms the acidity or
alkalinity of a solution. A solution with pH of 7 is neutral. A solution with pH below 7 is acidic and a
solution with pH above 7 is alkaline.
By electrolysis, the WATERMAID® Cell produces sodium hypochlorite (NaOCl), which in water
dissociates into sodium (Na
+
) and hypochlorite (OCl-) ions. It is the hypochlorite ions that then form
with the hydrogen (H
+
) ions (from the water) to form
hypochlorous acid (HOCl), the active agent
that destroys bacteria and algae, and oxidizes organic matter.
The chart (below) shows the effect of pH on the reversing reaction of HOCl in water. The greater the
percentage of active HOCl molecules in the water, the better the sanitising effect. From the chart, it can
be seen that at pH between 3 and 7, the percentage of active HOCl molecules in the water is at its
highest, although it is not suitable for swimming because the water is acidic.
Marblesheen, pebbled, quartzon and tiled pools stabilise naturally between pH 7.6 and 8.2 so
the
effects of chlorine are disadvantaged
.
For these pools it is recommended that pH buffer
(sodium bicarbonate)
be used as this will help stabilise the pH between 7.6 and 7.8, as well as raise
the total alkalinity.
Total alkalinity
is a measure of the alkaline chemicals in the water such as bicarbonates and carbonates.
It affects the speed and ease of pH change. If the total alkalinity is too high, keeping the pH within the
desired range is difficult.
Keeping the total alkalinity between 150 and 200 ppm will help keep
the pH below 7.8.
Adding sodium bicarbonate will also help to protect newly-surfaced marblesheen, pebbled, quartzon and
tiled pools, as it will react with calcium salts and form a coating of calcium carbonate over the surface.
This in turn will slow down the leaching out of lime from the fresh cement (which contains up to 60%
calcium oxides), thereby making it easier to achieve the desired water balance.
For an average sized pool, about 10 Kg (approx. 22 lb) of sodium bicarbonate will raise the total
alkalinity 80 ppm.
The pH remains stable and within the required range for pools with inert surfaces such as
fibreglass, fibreglassed concrete, painted concrete and vinyl-lined surfaces, which also have
a naturally occurring total alkalinity of 80 - 100 ppm. As this is an ideal situation, there is no
need to add pH buffer to these pools.
If hydrochloric acid is to be used to lower pH, it should be added SPARINGLY and only according to the
instructions given by an ACID DEMAND Test Kit. Any excess acid will attack the pool walls causing
calcium to be released into the water, which will then build up on the electrodes.
The ideal pH range for swimming
conditions is between 7.2 and 7.8.
It is important to note from the chart that
at pH 8.0, the chlorine in the water will
only be 21% effective.
A pH above or below the ideal range can
also cause irritation to the eyes and skin.
Ideal Range
7.2 - 7.8
Acid
Neutral
Alkaline
pH SCALE
Total
%
of
ACTIVE HOCl
molecules
Total
%
of
no
n-active
OCl
ions
THE EFFECT OF pH
ON HYPOCHLOROUS ACID
pH
1 2 3 4 5 6 7 8 9
0
20
40
60
80
100
100
80
60
40
20
0
Copyright © Watermaid Pty Ltd
18
TROUBLESHOOTING
LIGHTS DISPLAYED
Copyright © Watermaid Pty Ltd
100% CHLORINE PRODUCTION
LOW RANGE CHLORINE PRODUCTION
* Winter time / cold water temperature
* Low salt level
* Build up on cell electrodes
* Cell electrodes worn out
FLASHING BLUE LIGHT -AUTO CLEAN MODE
* Factory preset to 5 min / hour, after the first hour
SOLID RED LIGHT
* Salt level above recommended level and/or hot water
temperature in the pool. To rectify, when all lights light up,
press the minus ("-") button 2 - 3 times, so that the
WATERMAID® is not running at 100%.
* Check there is no metal contact between the 2 electrodes.
FLASHING RED LIGHT
* Water flow problem.
* Gas sensor error. Check sensing tang is clean and free of
deposit; the white wire is connected inside the black junction
box properly (metal to metal); and that the white wire is not
water damaged or affected by corrosion.
FLASHING AMBER LIGHT
* The red & black Cell wires are either matched incorrectly
inside the junction box or water damaged / affected by
corrosion.
* There is a break in the black wire.
* After heavy rain, a layer of rain water, which is less dense
and contains little salt will be at the top and feeding into the
electrolytic Cell.
* No load (Cell dead).
* Standby mode - press the plus ("+") button to make a
selection.
FLASHING RED & AMBER LIGHTS IN SEQUENCE
* There is a break in the red wire.
Red
Amber
Amber
Amber
Green
Green
Green
Green
Green
Blue
DISPLAY LIGHTS - LAYOUT
