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Copyright © 2017 Watermaid Pty Ltd
Version 20170223
13.4
Zero Chlorine
If the recommended level for residual chlorine cannot be obtained, check the following:
(i)
If an algaecide with main constituent "benzalkonium chloride" has been added to the pool within the
last 4 weeks. Most algaecides contain ammonium compounds (approximately 20%), which will react
with chlorine to leave a zero chlorine reading in the water. As a guide, about nine (9) times the
amount of ammonium compound in chlorine will need to be produced or added before there is a free
chlorine level in the water. Any debris in the water will need additional chlorination.
(ii)
If the filter is functioning properly. Take a sample of pool water in a clear glass and hold it up to the
light. Floating debris will indicate that unfiltered water is getting back into the pool. Please note: The
sand in a sand filter should be replaced around every five (5) years as the edges become rounded over
time due to the constant abrasion during filtering and will not work as effectively.
(iii)
With sufficient running times, the WATERMAID® chlorinator should be able to maintain a clean clear
pool for about a 20 bather/hour ratio (e.g. 4 people/5 hrs, 10 people/2 hours etc). It is important to
note that contamination from sunscreen, urine and pets will dramatically destroy the chlorine.
(iv)
Incorrect pH. Chlorine is not effective outside the correct pH range.
13.5
The Langelier Index
The Langelier Index calculation table (below) can be used to check the water balance of a pool. Readings of
pH, water temperature (TF), calcium hardness (HF) and total alkalinity (AF) are needed. These readings are
used to obtain the corresponding factor readings from the table (below) and then, to perform the Langelier
Index calculation.
For example, if pool water had the following values; pH 7.4, temperature 24°C (or 75.2°F), calcium hardness
100 ppm, and total alkalinity 200 ppm, then the Langelier Index calculation would be worked out as follows:
Start with pH
Add TF
Add HF
Add AF
Subtract (K=12.1)
+7.4
+0.6
+1.6
+2.3
-12.1
Langelier Index =
-0.2
If the result is between -0.2 and +0.2, then the pool water is in balance.
If the result is lower than -0.2, then the pool water is corrosive.
If the result is higher than +0.2, then the pool water is scale-forming.
To rectify corrosive water, the total alkalinity will need to be raised by adding sodium bicarbonate. To rectify
scale-forming water, the total alkalinity will need to be lowered by adding hydrochloric acid or white vinegar.
Please refer to the product labels for the quantity required. For white vinegar, about two (2) litres equates to
300mL of hydrochloric acid.