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Noticing an unsightly white film forming on the side of your pool? That’s calcium scaling and a good sign the pH and calcium levels of your pool are imbalanced.

What is Calcium Scaling?

An excess of calcium in the water can result in a white or white-grey scale forming on the pool’s surface and in the plumbing. It may also cause the water of your pool to become slightly cloudy from the calcium dust. Too little calcium, on the other hand, can degrade the surfaces below the waterline that contain calcium such as plaster, concrete, quartz, stone or tile. In this case, you may notice pitting or deterioration of the material.

Calcium scaling typically occurs because the pool water is of a high pH. Other causes of calcium scaling include high alkalinity, a high concentration of calcium or constant temperature changes and rapid evaporation.

Types of calcium scaling

If you’re concerned your pool is suffering from calcium scaling, you’ll need to understand what type of calcium build up you’re experiencing as there are different ways to remove each.

Calcium carbonate:

Calcium carbonate is white and flaky in appearance. It’s also relatively easy to remove.

Calcium silicate:

Calcium silicate appears white-grey and is a little more difficult to remove. This is because calcium silicate takes longer to form and if you can see it on your pool’s surface, it’s also likely to be inside the pipes.

To determine which type of calcium you have forming on your pool surface, us a couple of drops of muriatic acid. If its calcium carbonate, fizzing and foaming will occur as the acid reacts with the scaling. This reaction will not be seen where there is calcium silicate.

Pool by Wax Design Space featuring Andorra limestone and Coolum Random Ashlar stone walling
Pool by Wax Design Space featuring Andorra limestone and Coolum Random Ashlar stone walling

How to remove calcium carbonate scaling

Using a pumice stone should easily remove any calcium carbonate build-up. It’s important to note, pumice stones should only be used on hard surfaces like concrete or tile. This is not suitable for vinyl or fibreglass pools. Keep both the pumice stone and treated surfaces wet to prevent scratching.
You could also try a stain remover or eraser to get rid of the calcium carbonate. Most are safe for all pool surfaces however, it’s best to check with your supplier and follow the product’s instructions.
Another way to remove calcium carbonate is by acid washing your pool to lower the pH. This does, however, require draining your pool and is considered one of the more difficult ways to remove calcium scaling.

How to remove calcium silicate scaling

Calcium silicate can be removed by using a pumice stone and a whole lot of elbow grease. If you’re going to tackle this job yourself, a word of warning: calcium silicate build-up is notoriously difficult to remove.
Most professional pool cleaners will have a special chemical that will be able to remove the calcium scaling effectively.

How to prevent calcium scaling

If you’ve gone to the effort of removing calcium scaling, no doubt you’re keen to prevent the white film building up on your surface in the future. The key is to address the imbalance between the water’s pH and the calcium levels before it becomes a problem.

You can do this by:
• Reducing the pool water’s pH;
• Keep the Calcium Saturation Index (CSI) at the appropriate level;
• Remove excess calcium via a reverse osmosis treatment;
• Install a pool cover to help reduce evaporation.

For more advice on pools and pool maintenance, take a look at our Learning Library.

Feature image: Scala®  travertine pool by Maroondah Landscapes

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