Calcium on fibreglass pools

Calcium on fibreglass pools – We can help

In most cases, our treatment kit will completely remove white calcium on fibreglass pools.  It also restores the smooth blue finish and has prevention products to help keep it clean and looking like new. However, if left untreated, this white build-up will spread across the pool and become thicker and more noticeable over time.  For this reason, we strongly suggest doing something about calcium as soon as possible.  Our products remove calcium formation without draining the pool water or acid washing the surface.  The engineered active ingredients work by softening, dissolving, and preventing new calcium formation.

Calcium build-up on fibreglass pool
Before After Calcium on Fibreglass The Pool Stain Removers 1Calcium on Fibreglass The Pool Stain Removers 2

The picture above shows heavy calcium formation in a fibreglass pool which our treatment removed within a few weeks.

The calcium treatment removed the buildup without draining the pool water or acid washing.  Our customer was thrilled with the result.

A thin layer of calcium scale has formed on the waterline of this renovated fibreglass pool.

Our fibreglass pool calcium remover fixed this issue without draining or acid washing.  Our customer was very happy with the result.

Before After

5 reasons calcium forms on fibreglass pools

We will now discuss each of these issues in more detail below.

1. Calcium build-up on the pool surface

High pH levels will cause calcium carbonate in the water to precipitate or bond to the fibreglass surface. When this happens, it often leaves a white gritty layer that looks much worse when dry.  As the picture shows, this white layer becomes very noticeable when the pool water drops below its normal level.

To help prevent calcium in fibreglass pools, regularly test the pH and calcium hardness levels of your pool water.  Remember, high calcium (above 400ppm) often occurs for two reasons.  First, if you add too much calcium chloride (calcium increaser) to the water it will often lead to calcium formation. Secondly, calcium-based granular chlorine will increase the calcium hardness levels in your pool. Remember, if your calcium levels are rising for no reason, then it is likely that granular chlorine (calcium hypochlorite) is the cause.  Finally, if your tap water is hard (high in calcium) then this can also contribute to the issue.

Before adding calcium to your water, contact your pool manufacturer (not your pool shop) to find out what the calcium levels should be for your pool. Remember, each fibreglass pool brand suggests different calcium hardness levels.  And, check that your pool shop is aware that your pool is fibreglass and not concrete.

As the pictures show, our treatments remove calcium from fibreglass pools without draining the pool water or acid washing.

Salt Pools in Winter

Remember that saltwater chlorine generators continue to add free chlorine to the pool when they are running.  So, if a pool cover is protecting the free chlorine from sunlight then the chlorine levels will continue to rise if you cover your pool.  Consequently, the free chlorine levels can quickly rise to dangerous levels.  We have seen many cases where the free chlorine has exceeded 40 ppm in these situations. So if you are covering your pool, turn down the chlorine production because you won’t need much chlorine when you cover the pool.

Calcium on Fibreglass The Pool Stain Removers 5

This partially drained fiberglass pool shows the white calcium formation. Notice how thick and widespread it has become along the walls. This client did not attempt any type of treatment hoping that it would just disappear over time.

Fibreglass pools often pass through two phases as the surface begins to age.  Firstly, it is normal for the blue gelcoat colour to slowly fade to white over the decades.  This fading occurs because of chlorine, years of sunlight, and water chemistry imbalances which all age the surface. Remember, this slow colour loss, which often starts after 15-20 years, is normal. This is not a sign of a faulty pool interior or poor maintenance.

The second stage of ageing is when pools (25+ years old) start to develop a persistent white powder that appears when you brush the pool. This powder is actually a degrading gelcoat that has slowly broken down over time.  Remember, this powdery gelcoat will eventually disappear in sections of the pool revealing the lower layers of resin which are often dark brown. Finally, this surface breakdown is normal, particularly in high-use areas such as steps and ledges. Remember, the best way to extend the life of your fibreglass pool is to take care of the water.

calcium on fiberglass

This Fiberglass pool has a heavy layer of calcium formation on the surface. You can clearly see that the areas where the calcium has flaked away that the gelcoat color is in tact and not bleached. 

The layers of a fiberglass pool

The diagram below shows how the layers of material are bonded together. These layers are sprayed on by hand in the factory. Notice that most of the thickness of a fibreglass pool comes from the structure and not the blue decorative layer on the surface.

layers of gelcoat

This sectional diagram shows the layers of a fibreglass pool from top to bottom. Notice that the pool water can slowly circulate through the top surface layer of gelcoat. This process can allow the gelcoat to be effected by poor water chemistry.

gelcoat fading in fibreglass

As fibreglass pools age the blue top layer of gelcoat is worn away. This reveals the lower layers of brown fibreglass. This is not a stain, it is the fibreglass structure of the pool shell.

Bleaching in a fibreglass pool happens when the pH and the chlorine levels are both very high.  If the water remains at this level for a period of time, it may slowly bleach the pool surface.  Fibreglass pools should resist bleaching from mild water imbalance under Australian Standard (AS 1838:2021).  The chemical resistance test outlined in the standard is quite rigorous.  In short, the gelcoat must be able to withstand more than 100 times the normal chlorine level for 24 hours without any colour loss.  Remember, fibreglass cannot withstand unbalanced water or very high chlorine levels for long periods of time.  These extreme water conditions can sometimes result in permanent colour loss.

Gelcoat bleaching from unbalanced water is often smooth to touch and is non-responsive to cleaners and acids. In some cases, rubbing the surface with fine sandpaper can appear to remove this discolouration.  However, doing this will only remove the bleached Gelcoat layer in your pool. Remember, sanding the Gelcoat will leave your pool more susceptible to future staining and reduce the life of your pool surface.  Do not sand your fibreglass with any type of abrasive as this will cause permanent damage and may void your pool warranty.

Balanced water prevents fibreglass bleaching

Some pool owners believe that testing the water during winter (or when a pool cover is on) is not necessary. Often these same pool owners are horrified when they eventually remove the pool cover and discover extensive areas of surface bleaching. So, check your water during winter, even if you have the pool cover on.

Our treatments can sometimes help with surface bleaching.  However, there are often cases where nothing can remove the visual effects of pool surface bleaching.  Please contact us for further information if you feel your pool may have this issue.

Pool Cover Warning

Pool covers greatly reduce the amount of chlorine your pool consumes to keep the water clear. So, if you cover your pool for winter, remember to turn your chlorination levels down significantly!   If you don’t, the chlorine levels will keep rising through winter and bleach the fibreglass surface.  Covered pools often only need around 10% chlorine output during winter.  Remember to test the water during winter!

Gelcoat bleaching Fibreglass

Possible Gelcoat reaction with the pool water. Notice the smoothness of the white film and the distinct separation between the vivid blue and white along the waterline. Our treatments are sometimes effective with this issue.

In rare cases, the gelcoat can discolour and remain white if it has not cured properly during manufacturing.  So, if your pool has this issue, it will often become obvious within hours after you fill your pool with water. This occurs because the uncured surface is very porous, which allows the water to absorb into the surface resin and bleach the gelcoat. In fact, the impact of this bleaching is often permanent and unfixable. Because of this, you will need to re-fiberglass the entire surface of the pool to resolve this problem.

If an undissolved alkalinity increaser (aka buffer or sodium bicarbonate) is sprinkled directly into the pool, it can cause a stubborn white film to bond to the pool surface. So, to avoid this, ensure that the buffer is completely dissolved in a bucket of water before it is added to the pool.  Remember, when buffer is first added to water it will start as milky white and then as it continues to dissolve, the water will become clear within minutes. After that, once the water is clear then go ahead and add the buffer to the pool.

Don’t Drain or Acid Wash a Fibreglass Pool

In most cases, acid washing makes no lasting difference to the appearance of fibreglass pools.  But, if you insist on draining, use a licensed and insured professional to do this work.  This is because your pool walls will need to be cross-braced and secured to prevent buckling and cracking when you release the water. Remember, if your empty pool gets pushed up through hydrostatic ground pressure, you will need the contractor’s insurance to pay for a new poolAlso, you cannot simply push the pool back down if an uplift occurs.  Above all, please don’t drain a fibreglass pool, it is never a good idea.

Pool walls buckle inward from ground pressure. Photo credit: APCO Pool Specialties

Pool walls buckle inward from ground pressure. Photo credit: APCO Pool Specialties

Swimming pool pushed upward while empty. Photo Credit: Pool Water Recycling

Swimming pool pushed upward while empty. Photo Credit: Pool Water Recycling

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