Calcium on fibreglass pools – We can help

In most cases, our treatment kit will completely remove white calcium on fibreglass pools.  Our products also restore the smooth blue finish and have prevention products to help keep it clean and looking brand 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.  Our engineered commercial grade products work by softening, dissolving and preventing calcium formation from returning later on.

Calcium on Fibreglass The Pool Stain Removers 1
Calcium 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.

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

5 reasons calcium forms on fibreglass pools

  1. Calcium build-up on the surface.
  2. Pool interior is ageing (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 surface.

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

1. Calcium build-up on the pool surface

High pH levels in the pool water will cause calcium carbonate in the pool water to precipitate or bond to the pool surface. When this happens, it often leaves 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 in fibreglass pools, we suggest regularly testing the pH and calcium hardness levels of your pool water.  Remember, High calcium (above 350ppm) often occurs for two reasons.  First, too much calcium chloride (calcium increaser) has been added to the pool water. When this happens it often leads 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 directly (not your pool shop) to find out what the 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 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.

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.

2. The pool interior is ageing

Fibreglass pools typically pass through two phases as the surface begins to age.  Firstly, the gelcoat blue colour will slowly fade to white over time.  This fading typically occurs because of chlorine in the water, years of sunlight and water chemistry imbalances which all take their toll on the surface. Remember, this colour loss, which often starts after 15-20 years, is normal. This is not an indication of a faulty 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
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.

The second stage of ageing is when fibreglass pools (25+ years old) start to develop a persistent white powder that appears when the pool is brushed.  The 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 surface breakdown is normal, particularly in high friction areas such as steps and ledges. Remember, the best way to extend the life of your fibreglass pool is to maintain the water correctly.

3. Bleaching of fibreglass or gelcoat 

Bleaching in a fibreglass pool happens when the pH and the chlorine levels are both very high at the same time for a period of time. Remember, if the pool water remains unbalanced it may start slowly bleaching the pool surface.  Although fibreglass pools are required to resist bleaching from mild water imbalance under Australian Standard (AS 1838:1994), they often cannot withstand unbalanced water or very high chlorine levels for long periods of time.

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 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. Remember, check your water during winter, even if the pool is covered.

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.

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.

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 climbing through the winter and bleach your fibreglass pool surface.  Covered pools often only need around 10% chlorine output during winter.  Remember to test the water during winter!

4. Gelcoat not cured correctly during manufacture

In rare cases, 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 after the pool is filled with water. This occurs because the uncured surface is very porous, which allows the water to penetrate into the surface resin and bleach the gelcoat.  In fact, the impact of this bleaching is often permanent and cannot be fixed. Consequently, the complete resurfacing of 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 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 completely clear within minutes. Finally, once the water is clear then go ahead and add the buffer to the pool.

Do Not Drain or Acid Wash your Fibreglass Pool

In most cases, acid washing makes no lasting difference to the appearance of fibreglass pools.  However, if you insist on draining, we suggest using a licensed and insured professional to do this work.  This is because your pool walls will need to be properly cross-braced and secured to prevent buckling and cracking when the water is released.  Finally, if your empty pool is forced upward through hydrostatic ground pressure, you will need the contractor’s insurance to pay for a new pool. Remember, you cannot simply push the pool back down if uplift occurs.  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

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
  • 3.5 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 $295 for pools 55,000+ 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
  • 3.5 Kgs of our granular calcium dissolving compounds
  • 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 $455 for pools 45,000+ Litres


Enquire now!