Copyright © 2017Watermaid Pty Ltd
Version 20170223
- 29 -
The Langelier Index was originally designed to protect boiler feed devices, such as steel boilers in steam
engines, although it has been adopted by the pool industry as a means of determining non-scaling water in
swimming pools. When using the Langelier Index to balance water in swimming pools with electrolytic
chlorinators, never use calcium compounds; only use sodium bicarbonate or hydrochloric acid.
Please Note
: the use of sodium bicarbonate in an inert-surfaced pool (fibreglass, fibreglass concrete, painted
concrete or vinyl-lined) is unnecessary as the unchanging calcium level means that the total alkalinity
becomes a function of pH and water temperature and will then find its own equilibrium with time.
The ideal water balance is listed in the following table.
Water Temperature
15°C - 30°C (59°F - 86°F)
PH
7.2 – 7.8
Calcium Level
120 - 250 ppm
Magnesium Level
> 20 ppm
Isocyanuric acid
30 - 50 ppm
Total Alkalinity
> 150 ppm
To maintain water in balance for marblesheen, pebble, quartzon and tiled pools, the total alkalinity should be
greater than 150 ppm if the pH is to be kept below 7.8.
13.6
Algae
A common problem for any type of pool is algae growth. There are 24,000 known types of algae, all
distinguishable by being single-celled organisms capable of photosynthesis (they produce their own food),
mitosis (all cells can divide) and meiosis (reproduction is possible by combining with other algal cells).
The ideal environment for algal growth is when there are periods of zero chlorine. Algae blooms can take less
than a day to turn a pool green.
