Technical instructions
ZELIA ZLT
10
6.3. Controlling the TAS/TH
At the time of installation, you are advised to test the TAS (Total Alkali Strength) and/or the TH
(Total Hardness) of the pool water, or arrange for them to be tested by a specialist. The two mea-
surements are generally close and are more often than not expressed in French degrees (°F). If the
TAS and TH are different, use the average value of these two measurements. It is important to note
that very soft water (TAS/TH < 10°F) has the advantage that scale can be prevented but, on the other
hand, it is highly corrosive and its pH is very unstable. Conversely, very hard water (> 35°F) has a
pH which is very difficult to correct, and it is very irritating to the skin and causes scale formation
quickly on the installations. In extreme cases, you are therefore recommended to correct the TAS
and TH by using suitable chemical products.
6.4. Controlling the pH
The pH or Hydrogen potential measures the degree of acidity of the water. Its value is between 0 and
14. A solution with a pH of 7 is neutral. If it is lower than 7, the solution is said to be an acid and if it
is greater, the solution is said to be a base or alkaline. For the comfort of swimmers, the effectiveness
of the treatment and reliability of the installation, the pH of the pool water must be maintained at
about 7. It is generally thought that a pH between 6.8 and 7.4 is ideal. Excessively acidic water
(pH < 6.8) attacks mucus membranes, corrodes metals and can damage plastics. Excessively basic
water (pH > 7.4) can also be aggressive (caustic) and considerably reduces the effectiveness of the
chlorine. Therefore, when the pH goes from 7.2 to 8.2, the percentage of active chlorine goes from
70% to 20%.
To achieve maximum efficiency from the
ZLT
, the pH of the water should be maintained between
7.0 and 7.4.
As the water temperature varies during the season, the production time should be adjusted accord-
ingly. This adjustment of the production according to the temperature is carried out automatically
by the
ZLT
in the temperature controlled production modes (
P6
/
P7
)
