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pH/chlorine regulator AUTODOS 5000 - 2005-01-21
Eng_Autodos5000.doc ver 3.2 - page 26
4. General Description of Pool Water Cleaning
AUTODOS 5000 automatically monitors and controls the condition of swimming pool water maintaining the
chlorine and pH levels to desirable set values.
For effective bacterial control and sanitation of pool water it is essential to maintain the correct level of free chlorine,
but free chlorine readily combines with bather contaminants such as perspiration, cosmetics, hair lotions etc. and
becomes ineffective. Hence the need for continuous control and adjustment of free chlorine levels.
pH, which is a measure of the acid/alkaline balance in the pool water is also an essential element of pool water
control. When chlorine is added to pool water it produces two types of free chlorine, one fast acting and effective
(hypochlorus acid) and another which is slow acting and ineffective (hypochlorite ion). These two chlorine variations
are produced in a ratio determined by the level of pH, as the pH rises in value less of the effective free chlorine is
produced, and at a pH of 8.0 only 20% of the free chlorine produced is effective.
To regulate the correct chlorine level both pH and chlorine levels are monitored.
When chlorine gas is used for chlorine control the pool pH is lowered and a pH+ chemical (alkali) must be used to
correct the pH level.
When using either solid or liquid chlorine for chlorine control the pool pH is raised and a pH- chemical (acid) must
be used for pH correction. AUTODOS 5000 is suitable for both applications.
The figure below describes the relationship between hypochlorus acid and hypochlorite ions when the pH value is
altered. The figure is taken from 'Oregon Study - PPM or ORP: Which Should Be Used' by Jacques M. Steininger.
The content of combined chlorine can be lowered by using UV light or active carbon.