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White calcium on fibreglass

In most cases, our fibreglass treatment kit removes the white calcium on fibreglass pools and restores the smooth blue finish within a few weeks.  If left untreated, this white build-up will spread slowly across the pool surface and become thicker and more noticeable over time.  For this reason, we strongly suggest doing something about it as soon as possible.  Our calcium removal compound removes this calcium formation by softening and dissolving the build-up without draining the water, acid washing or scrubbing the pool.

Whitening or discolouration on fibreglass pool surfaces is normally a result of one of the following factors. We have ranked them in order from most common (1) to least common (5):

  1. Calcium precipitation (build-up) on the fibreglass surface.
  2. Pool interior is in final stages of aging (25+ years).
  3. Bleaching of colour from gelcoat interior.
  4. The gelcoat layer has not been cured properly in the factory.
  5. Undissolved buffer (alkalinity increaser) has bonded to the pool surface.

1. Calcium build-up on the pool surface

High pH levels in the pool water may cause any calcium present in the pool water to precipitate onto the pool surfaces leaving a white gritty layer.  As the picture shows, this white layer becomes very noticeable when the pool water drops below its normal level.

To help prevent calcium formation, we suggest regularly testing the pH and calcium hardness levels in your pool water.  High calcium (above 350ppm) often occurs for two reasons.  First, too much calcium chloride (calcium increaser) has been added to the pool water.  Consequently, many furious pool owners tell us that their calcium issues started after they were incorrectly advised by their pool shop to add too much calcium chloride to their fibreglass pool. Second, the use of a calcium-based granular chlorine has increased the calcium hardness level. If your calcium levels seem to be rising for no reason, then it could be that the use of granular chlorine (calcium hypochlorite) is the cause.

Before adding any calcium to your pool water, we suggest contacting your pool manufacturer (rather than your pool shop) to find out what the recommended calcium levels should be for your pool. This is because each fibreglass pool brand recommends different calcium hardness levels.  Also, check that your pool shop water testing software shows that your pool surface is fibreglass and not concrete.

As the pictures show, our treatments can remove calcium build-up from fibreglass pools without draining water or acid washing.

Calcium on Fibreglass The Pool Stain Removers 5
This partially drained fibreglass 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.

These pictures show calcium formation in a fibreglass pool which our treatment has removed without draining the pool water or acid washing.  Our customer in Western Australia was thrilled with the result.

2. The pool interior is ageing

Fibreglass pools typically pass through two phases as the surface begins to age.  The first is when the gelcoat colour slowly fades to a white colour over time.  This fading typically occurs because of chlorine in the water, years of sunlight, water chemistry imbalances and ageing. So the combination of these things will cause the coloured pigment within the gelcoat resin to slowly fade away.  Again, this colour loss, which often starts after 15-20 years, is normal and is not an indication of a defective pool interior.

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
Worn gelcoat in fibreglass pool

The second stage of aging is when many fibreglass pools (30+ years old) start to develop a persistent white powdery substance which appears when the pool is brushed.  The white powder is actually degrading gelcoat which has slowly broken down over time.  This powdery gelcoat will eventually disappear in sections of the pool revealing the lower layers of resin which are often dark brown. This gelcoat breakdown is normal, particularly in high friction areas such as steps and ledges.  The best way to extend the life of your fibreglass is to consistently maintain the water correctly.

3. Bleaching or fading of colour in gelcoat interior

Bleaching in a fibreglass pool can occur when the pH and the chlorine levels are both very high at the same time. Moreover, if the water remains in this state, it may start bleaching the colour out of the gelcoat.  In fact, fibreglass pools are required to resist bleaching due to mild water imbalance under Australian Standard (AS 1838:1994).  However, in extreme cases of water imbalance, the gelcoat coloured pigment is unable to withstand the unbalanced water and fading can occur.

Discolouration from unbalanced water is often very smooth to touch and is non-responsive to any cleaning method.  In some cases, rubbing the surface with fine sandpaper can appear to remove this discolouration.  However, by doing this, what is removed is the bleached gelcoat layer and the staining. However, sanding the gelcoat will leave the pool more susceptible to future staining and dramatically shorten the life of your pool.  Therefore, do not sand the fibreglass surface with any type of abrasive as this will cause permanent damage and void your pool warranty.

Some pool owners believe that testing the water during the cooler months (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 surface bleaching. So please check your water during winter even if it is covered.

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

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.

4. Gelcoat not cured correctly during manufacture

In rare circumstances, the gelcoat can discolour and remain white if it has not been cured properly during manufacturing.  So if your pool has this issue, it will often become obvious within the first few hours or days after the pool is filled with water. This discolouration occurs because the uncured surface is very porous, which allows the water to quickly penetrate deep into the gelcoat resin and bleach the gelcoat.  In fact, the impact of this bleaching is often permanent and cannot be fixed. Consequently, the complete resurfacing the fibreglass is required to resolve this problem.

5. Adding undissolved buffer to the pool

If undissolved alkalinity increaser (aka buffer or sodium bicarbonate) is poured directly into the pool, it can cause a stubborn white film to appear on the fibreglass surface. To avoid this, ensure that the buffer is completely dissolved in a bucket of water before it is added to the pool.  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 in a few minutes. So once the water is clear then add it to the pool.

Do Not Drain or Acid Wash your Fibreglass Pool

We absolutely DO NOT recommend draining or acid washing fibreglass pools – ever.  This is because we have found over the years that even after the expensive acid washing process has taken place, there is no lasting difference to the appearance of the pool surface.  However, should you insist on draining, we suggest using a licensed and insured professional to do this work.  This is because the pool walls will need to be properly cross braced and secured to prevent buckling or cracking as the water is released.  Finally, if the empty pool is forced upward through hydrostatic ground pressure, you will need the contractor’s insurance to cover the cost of a new pool. Also, you cannot simply push the pool back down if hydrostatic uplift occurs.

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

OPTION 1 – Calcium Removal DIY kit

What We Do 1


Calcium Stains in Swimming Pools The Pool Stain Removers 3


Calcium Stains in Swimming Pools The Pool Stain Removers 5



  • 1 Litre of our powerful calcium release and prevention formula
  • 4 Kgs of our granular calcium dissolving compounds custom made for your stain
  • Phone support from our technicians
  • Simple step-by-step instructions included
  • Pool does NOT need to be drained
  • Kit is sent and electronically tracked by Fastway Couriers
  • Kids are back in the pool in just 7 days
  • Kit is $285 for pools 45,000+ Litres


Enquire now!

OPTION 2 – Calcium Removal – On Site Technician


Calcium Stains in Swimming Pools The Pool Stain Removers 3


Calcium Stains in Swimming Pools The Pool Stain Removers 5



  • 1 Litre of our powerful calcium release and prevention formula
  • 4 Kgs of our granular calcium dissolving compounds custom made for your stain
  • Complete 7 point on site water testing
  • Your pool does NOT need to be drained
  • Kids are back in the pool in 7 days
  • Visit is $405 for pools 45,000+ Litres


Enquire now!