Understanding the chemical levels in the water
Although every bath is different, there are some general rules when it comes to bathing water chemistry which can be applied to baths of all shapes and sizes.
Here is a more in depth guide to balancing water levels. Your water testing kit should also contain information about the optimum levels you are hoping to find through testing.
| CHLORINE: Ideal chlorine level in a pool is 1-3 ppm. |
Chlorine is widely recognised for its disinfecting properties. When added to water, it effectively kills bacteria, viruses, & other microorganisms that can cause diseases and infections. If the level is a bit too low, then it’s just a case of upping the dose a little. On the other hand, if you find the levels of chlorine are too high, then stop dosage and dilute by adding water until the bath returns to the correct levels. |
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PH BALANCE: Ideal pH range is 7.2-7.6, with the optimum measure at 7.4. |
pH is a key test for water acidity or alkalinity. Low pH causes eye and skin irritation and corrosion to the bath. High pH causes cloudy water and lessens the effect of chlorine.
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| ALKALINITY: The alkalinity level in the water should be between 80-120 ppm |
Alkalinity and pH are closely linked. With low alkalinity pH levels can swing back and forth between too high, and too low. It’s not uncommon for these numbers to shift drastically causing an unbalance in your pools pH. Adjusting the alkalinity is a simple task if you have the right products. you may find that once you’ve adjusted alkalinity, you then have to go back and look at pH again. |
How to action the water testing results
| Monitoring free chlorine levels in your pool water |
Free chlorine involves the amount of chlorine that's able to sanitise contaminants, while combined chlorine refers to chlorine that has combined directly with the contaminants. Total chlorine is basically the sum of free chlorine and combined chlorine It will be easier to maintain the correct levels of free chlorine in a bath which is well-maintained and which is not allowed to become overloaded with bathers. The upper safe limit for free chlorine is 3mg per litre and if this level is passed, then chlorine dosing should be reduced. If the levels still rise, then the bath should the closed and the water diluted. |
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Recommended combined chlorine levels |
Combined chlorine refers to chlorine that has combined directly with the contaminants. The onboard UV will also reduce free chlorine levels. The levels of combined chlorine levels should be under 50% free chlorine, and never more than 1mg per litre. If you are finding unsuitable ratios of combined to free chlorine, then you may need to dilute the water. | |
| Water pH levels | The ideal pH range is typically 7.2 to 7.4. If you find levels higher than this, then levels of free chlorine have to be increased to ensure it is working effectively. | |
| Controlling water alkalinity |
Alkalinity levels ensure that the pH level is stable when acid-based disinfectants are used to clean the water. The PWTAG guidance recommends that levels of alkalinity should be stable at between 80mg and 200mg per litre. Alkalinity should be tested weekly, and there are plenty of commercially available kits to help operators with this task. Dilute acid can be used to lower the levels of alkalinity in the pool water where required or the water can be diluted. |
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| Managing calcium hardness levels in your pool |
Calcium hardness in the water should be between 75mg and 150mg per litre, but in areas with hard water this can be very difficult to achieve. It is therefore important to make sure that any chemicals you are adding in to disinfect the pool do not make the water even harder and increase the levels of calcium. If you are regularly finding levels of calcium hardness at over 300mg per litre, this can cause scale to build up on the pipes which can cause blockages and also affect the pH and temperature. Measurements of calcium hardness should be taken each week, using commercial kits and testing tablets. |
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| Testing for Total Dissolved Solids (TDS) |
High levels of total dissolved solids (TDS) can be destructive and should be avoided. Levels should be kept under 1000mg per litre. If necessary, TDS levels can be reduced by dilution. TDS measurements should be taken weekly, using an electronic meter which has been correctly calibrated. |
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| Testing for sulphates |
Sulphates also should be tested weekly, with levels ideally being less than 360mg per litre. |
The importance of water balance
The key to successful pool water maintenance is keeping all of those different factors in balance. One way of looking at the overall balance of the water in your pool is with the Langelier Saturation Index (LSI), a special formula which brings all of the different elements together. Best practice is to calculate the result weekly, at the same time as measuring alkalinity, TDS and calcium hardness.
What is the Langelier Saturation Index?
The Langelier Saturation Index is an approximate measure of the degree of saturation of calcium carbonate (CaCO3) in water. It is calculated using pH (Hydrogen Ion), Alkalinity (CaCO3), Calcium concentration, Total Dissolved Solids (TDS), and temperature of a water sample.
The Langelier Index (LSI) is calculated as follows:
LSI = pH – pHs
pH – pH Value
pHs – Saturation pH