Hanna Instruments HI 83216-01 - Manual (Page 5)

5
THE WATER BALANCE AND LANGELIER INDEX (LI)
The pool water characteristics need to be maintained in a balanced condition to avoid system failure. Measuring
the water balance is extremely important to predict if the water is corrosive, scaling or balanced.
A saturation index developed by Dr. Wilfred Langelier is widely used to predict the balance of swimming pool
waters. It is an estimation of the solutions ability to dissolve or precipitate calcium carbonate deposits. A certain
level of this precipitation (filming) is desired to insulate pipes and boilers from contact with water. When no
protective filming is formed, water is considered to be corrosive. On the other hand scaling does cause failure
because of incrustation problems.
In the treatment and monitoring of pool water, the pool manager must ensure that related parameters as
alkalinity, hardness and pH are duly taken into consideration.
Calcium Hardness
The presents of calcium in the system is desired to ensure filming on those places where the temperature is
relatively high, like in boilers and pipes transporting warm water. Scaling must be avoided because it reduces
heat transfer and pump capacity. Beside the calcium carbonate deposits in the pipes, high scaling values do
cause cloudy water.
It is recommended to maintain the calcium hardness value within the range from 200 to 400 ppm as calcium
carbonate (CaCO
3
).
Alkalinity
Alkalinity is the measure of the total concentration of alkaline substances, mostly bicarbonates, dissolved in the
water. The higher the alkalinity the more resistant the water is to pH change, the alkalinity
buffers the water.
At the same time, high alkaline water is a major contributor to scaling problems like incrustation in filtration
equipment, pumps, and piping.
It is recommended to maintain the alkalinity value within the range from 80 to 125 ppm as calcium carbonate
(CaCO
3
).