What is Alkalinity?

Alkalinity is a measure of the amount of alkaline material in the water, usually present as bicarbonates, pH carbonates and hydroxides. The amount of alkali in the water will determine how easy it is for changes in pH to occur.

The Alkalinity or temporary hardness is what prevents a change in ph (otherwise known as a buffer) in your pool. The recommended level is approximately 100ppm. To raise your alkalinity add Buffer (Sodium Bicarbonate) and to lower it use Soda Ash (Sodium Carbonate). Acid is often used to lower alkalinity but it will not reduce the levels it will just appear to change them due to the method of testing used, but it will lower your pH significantly.

The pH is critical for water balance and by increasing your alkalinity you can buffer the pH in your pool so that it won’t fluctuate as easily. Just remember that when adding Buffer to a swimming pool to increase the alkalinity, it will also increase the pH, so you may need to add more acid.

One of the biggest influence on your pH and Alkalinity is the surface of your pool. Concrete, marblesheen and aggregate pools have a surface high in lime and calcium carbonate. Leaching from this surface will increase both the alkalinity and pH. This is why you will use more acid in a concrete pool. To help prevent this new concrete or pebblecrete pools should be dosed with 4-8kg of buffer when first filled. This will cause the surface to ‘seal’ reducing leaching. In fibreglass, vinyl or painted pools the sealed surface means that there is little influence on the water chemistry. This will result in usually lower pH and Alkalinity level. This is not a problem and is why Buffer is not really required in smooth surface pools.

An important thing to note is that when you adjust your alkalinity you will affect your pH. If you try our free software which uses the Langelier index to balance water you will discover that the alkalinity has a fairly minor impact on water balance in comparison to your pH. With a pH between 7.2 and 7.8 you can have an alkalinity anywhere between 30 and 300 without a problem. Tap water is usually around 30-40 which is why buffer is not regularly required in most pools.


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