Calcium in Swimming Pools

Remove calcium from pool without draining

It is often difficult to remove calcium from pool surfaces.  In fact, calcium is the most complex and difficult of all the issues we treat.  This is because it can form in a pool for a variety of reasons and is very hard and stubborn.  However, most of the time, white calcium spots (or scale) forms because of consistently high pH – particularly when the pool is new. High calcium hardness also plays a part in calcium formation.  So, if you have a new pool or live in an area with hard water, we suggest testing calcium hardness regularly.

Calcium buildup in pool interiors (the main causes)

Calcium spots
calcium scale and spots

Calcium spots can also form due to poor pool interior application.

This means that as the pool surface is applied in a new or renovated pool, voids (or air pockets) form under the coloured concrete layer. These pockets soon fill with water which then calcifies and grows under the surface. Then, as the calcium in the void continues to grow over time, it forces calcium out through the interior and into the pool, either through cracks or calcium nodules. These nodules often look like calcium is dribbling down the pool walls and can sometimes look like icicles. There is more information about nodules at the bottom of this page.

If you have a fibreglass pool with white calcium buildup, we have a page dedicated to removing calcium from fibreglass pool surfaces here.

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Typical signs of calcium scale and spots

calcium scale and spots

Remove calcium without acid washing

You don’t have to drain or acid wash your pool to remove calcium from pool surfaces.  Our treatments almost always remove hard calcium deposits completely, without draining the pool or acid washing the surface. Our powerful products are very effective in removing and preventing calcium deposits from Pebblecrete, Quartzon, vinyl-lined and fibreglass pools. Also, they include a long-lasting prevention product to help calcium away once it is removed.

Remember, acid washing removes most calcium but it will usually return within a few months if the water is not treated with our calcium preventative. The good news is that our treatment is a fraction of the cost of an acid wash and is far more effective. This is because we add the needed preventives to the pool as part of the treatment. For more about acid washing click here.

If you are unsure of the type or cause of your calcium issue please feel free to contact us first. There is more technical information about calcium below.

Calcium Stains in quartzon Swimming Pool
Calcium Stains in Swimming Pools The Pool Stain Removers 2
white calcium film on fibreglass
Calcium nodule

Calcium deposits in pool

There are several reasons why calcium deposits form in swimming pools which we discuss below. In short, calcium usually forms from poor workmanship during the pool surface application process or from poor water maintenance over time. However, even the experts around the world are not in full agreement on the exact causes of calcium formation.   Some experts say calcium is caused by consistently poor water chemistry.  While others argue that it is the poor surface application that is the cause.  However, if you maintain your pool water and brush the pool surface occasionally your chances of dealing with calcium are greatly reduced.

In almost every pool, calcium is either evident in the form of white balls or as elongated nodules. These nodules are approx. 2–3mm wide and 3–12mm long and can appear like icicles growing out of or ‘dribbling’ down the walls or floor of your pool. This type of formation may indicate that a section of the pool surface has de-laminated (pushed out) from the main pool structure. Remember, if the calcium spot reappears in the same place after being rubbed off, delamination is likely to be the cause. Please call us if you suspect you have calcium nodules, surface cracking or white calcium spots in your pool. This type of calcium build-up is often more noticeable in darker pool interiors.

Calcium can also form a thin calcium film that covers dirt or metal stains on the pool interior. Although calcium carbonate is white, in this case, it may look brown or grey because the dirt has discoloured and contaminated the calcium.  When this happens, the calcium staining will look brown or discoloured. Remember, this type of staining cannot be removed with chlorine or firm brushing because the calcium film over the dirt ‘shields’ the stains.

When high calcium causes calcium formation it is usually in the form of a light covering rather than spots.  In this case, calcium will often form blotchy areas that can look like swirl marks on the pool surface.   This film will often visually highlight the imperfections on the surface. For example, our clients will often say that their pool looked great when it was first filed, but later on, they can now see swirl marks, ridges or trowel marks that have appeared a short time later. Remember, this happens because calcium exacerbates the appearance of these issues. 

Calcium scale is a common issue in modern concrete pools as many pebble based pool surfaces now use white cement instead of grey cement. However, white cement contains up to 36% calcium hydroxide.  This contributes to the challenge of managing calcium. This is because the pool surface is now rich in calcium which increases calcium hardness and increases the pH of the pool water.  These factors will usually lead to a thin layer of calcium over the pool surface which continues to grow because it attracts more calcium to it over time. Remember, calcium will become thicker and sometimes harder than the concrete pool surface over time!

If you have calcium scale or spots, we strongly suggest you do something about it soon. This is because calcium that is left for long periods can lift, crack and break up your cement pool surface causing serious and costly damage. Sadly we often inspect pool surfaces that are almost completely destroyed by several large calcium spots that have been left to grow. Remember, our treatments help prevent this from happening by removing the calcium and stoping it from coming back.

In most cases, swimming pool surface applicators will add calcium chloride to the interior mix to accelerate the curing (drying) process.  Adding calcium causes the cement render to dry faster.  Also, adding calcium to the mix is also done to prevent the wet surface from ‘slumping’ or sliding down the walls during application.  Most importantly, adding calcium also helps the contractors can get to the next job faster!

We have found that some pool surfaces that have been applied on rainy days or during very cool weather often have more calcium chloride added to the mix to assist in the drying process. We are not suggesting that adding calcium is a bad thing, but certainly, an excess of calcium can be unhelpful and can lead to bleed water entrapment. It can also lead to calcium formation within the first few months of the pools life.  Furthermore, by speeding up the curing process too much, the concrete is not able to reach its optimum strength.     Should this occur then calcification of the pool surface may become evident in the future.  This type of staining can be removed with our products.

Some pool owners in the eastern states of Australia believe that the type of calcium they have in their pool is calcium silicate.  So, with the exception of Western Australia and South Australia, it is unlikely that there is enough silica within the source water to have any visible precipitation of calcium silicate.  For example, in Sydney water, there is less than 2 mg/L of silica in the city water supply.  This is a very low number which is roughly equivalent to 1 cup in an entire swimming pool.  So, this means that even if all of it precipitated at the same time, the chances of it being visible are very low.

On the other hand, calcium chloride, recommended in all pools, normally should run at about 250ppm. This means that there is around 20kgs of calcium chloride (90 cups) in your pool to bring the water to the right level.  Remember, the formation of calcium chloride is infinitely more likely in most situations.

For more in-depth scientific information about removing calcium from swimming pools click here.

Calcium stains 5

Calcium Stain Removal

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