It's all in the Chemistry

When your pool water is properly balanced, it means that your water’s chemical requirements have been met. If the chemicals are not in the ideal ranges, the water may affect other parts of your pool. To obtain the missing elements, it could attack or deposit additional elements on the pool surface or equipment. If left uncorrected, this can result in costly troubles down the line. Balanced water is also essential for an effective sanitising process as it kills bacteria and prevents algae growth.


Chlorine is the common sanitiser for your pool. Bacteria can grow in any untreated body of water with swimmers being the primary source of contaminants along with rainwater, leaves, grass, dust, and pets.

Having a sanitiser in the pool water at recommended levels will eliminate most of the bacteria in the water by basically tearing apart a germ, shredding its cell membrane and proteins.

The neutralised bacteria are then filtered out and any residual sanitiser left in the pool water will prevent any new bacteria growth.

A standard outdoor pool should have a chlorine level of 2.5 – 3.0 ppm (parts per million).


The pH reading tells us whether the water is acidic or alkaline and incorrect levels may cause itchy skin and red eyes. The pH level ranges from 0 to 14, with 7.0 being neutral. Values below 7.0 are acidic. When balancing swimming pool water, pH is probably the most important factor to consider. However, it is frequently overlooked.

The Australian Standard for pool water is between the range 7.0 to 7.8.  We recommend 7.2 to 7.6 for in-ground concrete pools, 7.0 to 7.2 for fibreglass pools and 7.6 to 7.8 for spas. It is important to check and adjust the pH level regularly after heavy rain, heavy pool use, topping up the pool, or adding chemicals, which changes the pH level and affects sanitising. 

The effect of pH variation is most noticeable on the effectiveness of your chlorine to sanitise your pool. A typical domestic pool will aim for a chlorine level of about 1-2ppm.

When your pool has a pH of 7, the free chlorine has 75% Hypochlorous Acid (active) ions. If your pool has a pH of 7.8, the free chlorine has just 28% Hypochlorous acid (active) ions, making your sanitiser much less effective.

As a result, a pool with a pH of 7 and a free chlorine level of 0.5ppm will have the same sanitizing effect as one with a pH of 7.8 and a free chlorine level of 1.35ppm. 

This is why the pH of your pool is important.

Total Alkalinity

This is a measure of bi-carbonates, carbonates, and hydroxides in the pool. We usually suggest 80ppm to 100ppm in swimming pools and 100ppm to 120ppm in spas is the accepted range, depending on the other balance factors. We can help you find the recommended level for your pool.

The corrosion of equipment and erosion of pool surfaces will result from low Total Alkalinity. In addition, a low Total Alkalinity can cause mild skin irritation and itchiness, and it will cause the pH levels to be very unstable, which will result in major shifts in pH with small additions of other chemicals.

Adding buffer (bi-carb soda) will raise Total Alkalinity, while hydrochloric acid will lower it, so these two chemical components must be adjusted simultaneously.

When topping up the pool, depending on the on the Total Alkalinity of the top-up water and the amount topping up, this will affect the Total Alkalinity of the pool water.

Calcium Hardness

The amount of calcium dissolved in your pool water is measured. For a typical concrete, marbelite or pebble pool, we recommend 250ppm to 350ppm of calcium. Typically, Calcium Hardness cannot be tested with the standard test kit, so you will need to bring in your water sample for testing.

Calcium levels in most pools are not naturally high, so you only need to test them a few times a year unless you use Calcium Hypochlorite to sanitise your pool. This chemical raises calcium hardness levels, so you may have to do more frequent testing and balancing.

As with Total Alkalinity, if Calcium Hardness is not maintained correctly, low levels will cause corrosion to the pool surfaces and equipment and high levels will lead to scale formation.


When there is no pool cover, cyanuric acid is used as a chlorine stabiliser to prevent chlorine loss caused by UV rays (sunlight).  Cyanuric acid should be added and maintained at 50 to 70ppm in the pool. To minimise degradation by UV light, it binds to free chlorine and then slowly releases it, which extends the time it takes to deplete each dose.

As the free chlorine is broken down by the UV light, the effectiveness of your sanitation will be reduced, which may lead to an increase in algae growth.

On the flip side, if you regularly use powdered stabilised chlorine to sanitise your pool, your stabiliser levels can get too high, and this can effectively block your sanitiser from being effective.

Interestingly, Cyanuric Acid is not consumed or lost from swimming pool water unless due to splashing, backwashing, or introduction of fresh water, these are the only times that you’ll need to add more Cyanuric acid.

For more information about your pool’s water balance, speak to one of our knowledgeable staff in store.

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