SPASA Recommends maintaining a pH level of 7.2 - 7.6 for most pools and spas, or 7.2 - 7.4 for fibreglass pools.
A pH level lower than 7.0 is acidic and may damage pool equipment and surfaces, and could also void equipment warranty.
Chlorine is less effective at higher pH levels, and pH levels greater than 7.8 are not recommended for this reason.
Adjusting the pH to the ideal pHs is often the easiest way to bring the LSI into equilibrium, except in cases where pHs is more than 0.2 outside of the recommended range.
Pool equipment such as pumps and heaters will usually have an acceptable pH range documented, and exceeding these limits may void the warranty.
(For private pools the Australian Standard1 is for pH levels to be maintained between 7.0 - 7.8)
1Australian Standard AS 3633-1989, Private swimming pools - Water quality. For information on water quality requirements for public pools and spas refer to HB 241-2002, Water Management for Public Pools and Spas.
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Generally the salt level (or salinity in ppm) will be a close enough approximation of TDS if regular pool salt (Sodium Chloride)
has been used, and relatively pure water has been used to fill the pool.
In cases where bore water has been used to fill the pool, or blended mineral salts are used then this becomes a little more complicated. In most cases the TDS has a relatively low impact on the LSI so an approximation is usually acceptable.
Note: Use of liquid chlorine may increase the TDS of the water over time.
Note: Salt Chlorination does not consume salt, however the salt level in the water is reduced over time by dilution of the water through rainfall and topping up with fresh water.
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The Australian Standard1 Recommends a range of 80 - 500ppm. Higher calcium levels may sometimes be beyond your control if your water supply has a high calcium level, resulting in a positive LSI and scale forming.
Adjusting the pH in your water to within 0.2 of the ideal pHs level may be sufficient to correct this. (So long as pHs is within the range 6.8 - 8.0).
Low calcium levels will generally result in a negative LSI which may damage pool surfaces and may be difficult to correct with the pH level alone, as the ideal pHs will often be too high.
Note: use of Calcium Hypochlorite (non-stabilised chlorine) will increase the Calcium Hardness of the water over time.
1Australian Standard AS 3633-1989, Private swimming pools - Water quality. For information on water quality requirements for public pools and spas refer to HB 241-2002, Water Management for Public Pools and Spas.
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The Australian Standard1 Recommends a range of 60 - 200ppm. Below 60ppm Total Alkalinity the pH level in the water will become difficult to control, as changes in bather load and the addition of chlorine or acid may cause the pH level to change dramatically and unpredictably.
The Total Alkalinity level in the water will generally fall over time (so long as the pH level is maintained correctly), and can be increased by adding Sodium Bicarbonate to the water (often referred to as 'pH Buffer' in the pool industry) or Sodium Carbonate (often called 'pH down' as it also has a greater effect on lowering the pH level)
Total Alkalinity levels above 200ppm are not recommended as this will cause the pH level in the water to constantly rise, resulting in increased acid demand and less effective chlorine.
SPASA recommends maintaining total alkalinity between 120 - 160ppm for pools, ans 60 - 150ppm for spas.
1Australian Standard AS 3633-1989, Private swimming pools - Water quality. For information on water quality requirements for public pools and spas refer to HB 241-2002, Water Management for Public Pools and Spas.
Langelier Saturation Index(LSI) Calculator
The Langelier Saturation Index (LSI) is a measure of a solution's ability to dissolve or deposit calcium carbonate (calcium scale).
In the swimming pool industry the LSI is used as an indicator for the corrosive or scale forming potential of the pool or spa water.
Excessive calcium scale forming on pool surfaces can be unsightly and difficult to remove, it can also reduce the efficiency of heaters and block filters.
On the other hand corrosive water can cause damage to heaters and other equipment, and it will tend to leech calcium from pool surfaces causing permanent damage.
The LSI is particularly useful for finding the ideal pH level for your pool, especially in the following situations:
- a high calcium level is present and beyond your control.
- calcium deposits forming on pool surfaces
- rapid calcification of chlorinator electrode
Notes:
- If the LSI is greater than 0.5, then the water will tend to precipitate a scale layer of calcium carbonate.
- If the LSI is less than -0.5, then the water will tend to dissolve solid calcium carbonate.
- Ideally the LSI of pool and spa water should be maintained between -0.2 and +0.2 to be in equilibrium, where it will neither form or dissolve scale.
Enter your water test results below, and press submit to calculate the Langelier Saturation Index
Calculations
Formula
Calculation
Result
LSI = pH - pHs
LSI = 7.600 - 7.559
LSI = +0.041
pHs = (9.3 + A + B) - (C + D) where:
pHs = (9.3 + 0.248 + 2.088) - (1.998 + 2.079)
pHs = 7.559
A = (log10(TDS)-1) / 10
A = (log10(3,000)-1) / 10
A = 0.248
B = (-13.12 * log10(deg C + 273)) + 34.55
B = (-13.12 * log10(25 + 273)) + 34.55
B = 2.088
C = log10(Ca2+ as CaCO3) - 0.4
C = log10(250) - 0.4
C = 1.998
D = log10(total alkalinity as CaCO3)
D = log10(120)
D = 2.079
Analysis
WATER IS IN EQUILIBRIUM WITH CALCIUM CARBONATE
The ideal pH for perfect equilibrium (pHs) is: 7.559
The pH level in the water is within the range recommended by SPASA of 7.2 - 7.6 The pH is close enough to the ideal pH for the LSI to be considered in equilibrium The Calcium Hardness in the water is within the recommended range of 80 - 500ppm The Total Alkalinity in the water is within the recommended range of 60 - 200ppm
Other factors
Free Chlorine and Total Chlorine
The Free Chlorine level in your water is the most significant factor to sanitation. It is recommended to maintain an average of between 1.0 - 3.0 ppm for all pools and spas.
The Total Chlorine level will generally be slightly higher, as this includes chloramines in the water. While chloramines are a secondary disinfectant, they are not as effective as chlorine and they produce a strong chlorine smell.
The presence of chloramines will also significantly increase chlorine demand in the water. If the Total Chlorine level is more than 0.5ppm higher than the Free Chlorine level, then a shock dose
of chlorine is recommended to burn out the chloramines. Once the chlorine level returns to normal, this will reduce chlorine demand and reduce the smell of chlorine in the water. Consult your local pool professionals for advise on this procedure.
Stabiliser (Isocyanuric Acid)
Recommended Range for outdoor domestic pools: 30 - 50ppm.
Reduces chlorine loss due to UV rays from the sun, especially in summer. Generally not required for indoor pools unless exposed to significant amounts of UV from sunlight.
Not recommended for spas or commercial pools. Never exceed 80ppm as this will reduce the effectiveness of the chlorine in the water resulting in unsanitary water conditions.
Note: Use of Sodium Dichloroisocyanurate (Stabilised Chlorine) will also increase the stabiliser level in the water.
