Calcium buildup on fiberglass pool
Calcium on your Fiberglass pool?
If your fiberglass pool has turned rough, white, or hazy, you’re not alone. Calcium buildup is the most common surface complaint we see from fiberglass pool owners. We can fix calcium scale before it damages your pool surface! Our engineered calcium treatment kit has four active ingredients designed specifically for fiberglass to dissolve all types of calcium, including:
- Calcium Carbonate
- Calcium Silicate
- Mineral scale
- White waterline calcium
- Calcium Hydroxide
Our treatment not only restores your pool’s surface color, but the included scale prevention polymer prevents the calcium scale from returning. Don’t wait for the buildup to thicken, treat it now to protect your pool surface from damage.
If left untreated, calcium spreads and becomes thicker, harder to remove, and will eventually damage the gelcoat.
Call us today. We can help.
Calcium scale on fiberglass pool
What causes calcium buildup on fiberglass pools?
- High Ph – When the pH of water exceeds 7.8 it can cause white calcium to fall out of solution and ‘plate out’ onto the pool surface causing it to appear white.
- High Calcium Hardness – When the calcium hardness of pool water exceeds 600ppm this saturation of calcium causes settling on the pool walls and floor.
- Calcium based chlorine – ‘Cal hypo’ is a granular chlorine made by blending chlorine with calcium. So, when you’re adding chlorine to the pool, you’re also adding calcium as well.
- Calcium hardness increaser – Some novice pool stores will tell their fiberglass customers to increase calcium above 120ppm. This often leads to calcium scale.
When pH, calcium hardness, or alkalinity are off balance, calcium and other minerals in the pool water will precipitate (deposit) on the fiberglass. This is why fiberglass pools often get covered in a rough, white layer forming on the surface, even when the pool is quite new. Our calcium removal kit removes this buildup without draining the pool.
Why fiberglass pools turn white
If your fiberglass surface looks white when the water drops, don’t panic, this is often just a thin layer of calcium carbonate/silicate that has bonded to the fiberglass. Our treatment kit will remove this layer of calcium.
Our treatment will:
- Remove calcium without draining
- Safe on all fiberglass surfaces
- No acid washing required
- Removes white ‘haze’ and scale
- Prevents calcium from returning
Our calcium removal kit does more than just clear buildup; it restores and protects your gelcoat while creating a 6-month barrier to help prevent future scaling.
To eliminate any chance of bleaching, we recommend maintaining a free chlorine level no higher than 2-3ppm. Fiberglass pools do not like high chlorine because very high chlorine causes permanent surface oxidation or bleaching.
How to Remove Waterline Calcium Scale
That white ring around your pool waterline is usually a result of heat and evaporation leaving behind concentrated calcium layer. Our treatment removes this thin buildup without damaging the pool surface.
Your pool’s blue gelcoat is very thin and delicate—much thinner than a credit card. We’ve seen many owners cause permanent, deep scratches by using scourer pads, steel wool, or abrasive DIY tools. Once the gelcoat has deep scratches, the damage is irreversible.
Our treatment kit avoids these risks by dissolving scale chemically, requiring no aggressive scrubbing. Our engineered formula uses a gentle erosion process to dissolve calcium away over a few weeks, keeping your pool surface protected.
Calcium Removal Options
Calcium Removal - DIY kit
- 1 bottle (64oz) of our calcium prevention formula
- 7.7 lbs of our calcium dissolving compounds
- Free phone support from our technicians
- Simple step-by-step instruction video included
- Pool does NOT need to be drained or acid washed
- Kit is shipped express and tracked by UPS
- Kids are back in the pool in just 7 days
- Kit is $295 for pools over 12,000 gallons
Calcium Removal –
On Site Technician
- (64oz) of our powerful calcium prevention formula
- 7.7 lbs of our granular calcium dissolving compound
- 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 $445 for pools 12,000+ gallons
Our Company Credentials
Why draining fiberglass pools is dangerous
Do not drain or acid wash a fiberglass pool to treat calcium buildup. Not only does this often fail to clear the scaling, but it also puts the structural integrity of your pool at risk.
Fiberglass shells are designed to be kept full and rely on the weight of the pool water to stay in place. This means that if the pool is empty, hydrostatic pressure pushes against the floor and walls causing structural damage.
If draining is unavoidable, ensure your contractor is fully insured and utilizes proper cross-bracing. Without these safeguards, your pool may suffer from:
- Wall Buckling and Warping: Permanent structural deformation.
- Cracking: Surface and structural cracks in the gelcoat and structure.
- Pool Shell Uplift: The pool “popping” or lifting up out of the ground -requires a full replacement.
- Floor ‘Heaving’: If water is trapped under the pool, the middle of the pool floor may feel soft or ‘bouncy’ once drained which may lead to stress fractures.
- Plumbing Damage: Fiberglass pool plumbing uses rigid PVC pipes. If the pool shell moves when drained, it can snap/fracture these pipes at the returns or drains. These leaks are very difficult and expensive to locate and repair.
Mineral Scale on fiberglass
For many pool owners, well water is the only available water source for filling their pools. Sadly most well water is high in calcium, iron, and magnesium. Over time, these minerals bond to the surface leading to roughness, brown stains, and discoloration. Our treatment targets and dissolves these minerals without the need to drain your pool water.
Pro tips for those using well water:
- Use a pre-filter when adding water to the pool from a well.
- Add Scale & Stain Eliminator every 6 months
- Use a metal removal product regularly to remove metals and iron.
Our Scale & Stain Eliminator is included in our calcium kits. When used every six months this preventive polymer prevents calcium and minerals from ‘plating out’ and keeps your fiberglass surface smooth and blue.
What Our Customers Say About Us
How to Protect your Fiberglass Pool Surface
For fiberglass pools, calcium and mineral sequestration is a critical defense to protect the pool surface. Unlike concrete pools, fiberglass has a thin, porous layer called the gelcoat. When pool water becomes saturated with minerals and calcium ions will precipitate onto the surface. Without a sequestering agent like Scale & Stain Eliminator, these ions “bond” within the microscopic pores of the gel coat, leading to a permanent, hazy white appearance – often mistaken for fading.
Our Scale & Stain Eliminator, works by chemically “dispersing” calcium and metal ions. This process, known as sequestration, keeps the minerals in a liquid state, preventing them from crystallizing on the pool walls.
Using a sequestrant every 6 months preserves the vibrant color and smooth texture of the fiberglass.
Causes of discoloration in Fiberglass Pools
Click headings below to see more
Calcium build-up on the pool surface
High pH levels
If your pH is too high, your pool water may cause soluble calcium to precipitate onto the pool surface. When this happens, it often leaves a thin white gritty layer on the fiberglass surface.
High Calcium Hardness
To help prevent calcium formation, test the pH and calcium hardness levels in your pool water. Remember, High calcium (above 600ppm) often can occur if too much calcium chloride (calcium hardness increaser) has been added to the pool water. When this happens, it leads to calcium formation.
Calcium based granular chlorine
Calcium-based granular chlorine will also increase the calcium hardness levels in your pool. If your calcium levels seem to be rising for no reason, then it is likely that the granular chlorine calcium hypochlorite is the cause.
Ask your pool manufacturer before adding calcium
Before adding extra calcium chloride to your pool, water, contact your pool manufacturer (not your pool store) and get the suggested calcium levels for your pool because each manufacturer suggests different calcium levels. Also, make sure that your pool store knows that your pool surface is fiberglass and not plaster. Plaster pools are much more common and require different water chemistry levels.
Prolonged neglect led to a heavy crust of white calcium across this fiberglass pool, leaving thick deposits everywhere. While the client hoped the scaling might resolve itself, the buildup only persisted. However, once treated, the results were remarkable. The surface itself still had most of the original color.
The pool interior is ageing
Gradual fading over time is normal
Fiberglass pools typically pass through two phases as the surface begins to age. First, the gelcoat blue color will slowly fade to white because of chlorine in the water, years of sunlight, and unbalanced water. All of these factors take their toll on the surface color. This color fading, which often starts after 15-20 years, is normal. This is not a sign of a faulty pool interior.
Gelcoat degradation
When fiberglass (20-30 years old) starts to develop a very fine white powder that appears when brushing or rubbing the pool this powder is usually degraded gelcoat. This powder will eventually disappear in sections of the pool, revealing the lower dark brown layers of fiberglass.
This is usually first noticed in high-friction areas such as steps and benches. So, if you start to see brown showing through, this is often an indicator of worn gelcoat and not a stain. Also, weird patterns and lines will start forming in the pool, as the picture shows.
This 25 year old fiberglass pool has light blue gelcoat that has worn away.
Under this worn gelcoat is the brown fiberglass used to make the pool structure.
You can clearly see the brown starting to show through where the gelcoat has worn away.
This pool will need a new interior coating.
Bleaching of fiberglass or gelcoat
Is my fiberglass pool bleached?
The Cause of Surface Bleaching. Bleaching in fiberglass pools typically occurs when pH, calcium, and chlorine levels remain excessively high simultaneously. While fiberglass is resilient, it cannot withstand prolonged chemical imbalances. High chlorine levels, in particular, will eventually oxidize the surface, leading to permanent fading.
Winterization Hazards Proper winterization is critical. Ensure your pool guy does not over-chlorinate the water immediately before closing. If high chlorine levels are trapped under a cover for months, the sustained chlorine exposure can cause severe, irreversible surface damage.
Misidentifying Calcium vs. Bleaching Bleached gelcoat is often smooth to the touch and unresponsive to standard cleaners or acids. A common mistake is attempting to sand the surface; while this may reveal a darker blue patch, you aren’t removing a layer of calcium—you are grinding away the protective gelcoat itself.
Warning: The blue gelcoat layer is incredibly thin—less than half the thickness of a credit card. Improper sanding permanently thins the pool shell, invites future staining, and significantly shortens the lifespan of your pool. Never use abrasives without professional guidance and approved products.
The “Hidden” Danger of Pool Covers Some pool owners believe that water chemistry doesn’t need to be checked if the pool is covered during winter. This often leads to a “horror story” reveals in the Spring when the cover is pulled back to show extensive bleaching and staining. A few water tests during winter is a great idea.
A pool cover protects the free chlorine from UV sunlight. So, when your pool is covered, the chlorine levels will continue to rise because the chlorine is now protected from UV light. We have seen many cases where the free chlorine has exceeded 40ppm in these situations.
If you’re covering your pool, make sure you reduce the chlorine dose significantly. You need almost no extra chlorine when the cover is on.
Can Bleaching Be Fixed? While our specialized treatments can often reduce the visual impact of surface fading, some oxidation is permanent. If the chlorine has completely oxidized the pigment within the gelcoat, the color cannot be “brought back” because the chemical structure of the gelcoat has been corrupted.
This pool suffered severe bleaching after being left covered for months with free chlorine levels exceeding 15 ppm. You can clearly see the original color where the hose is filling the pool—a stark contrast to the damaged surface. While water usually masks white scaling, this bleaching was so extensive that even when the surface is wet it makes no visible change.
The layers of a fiberglass pool
The diagram below shows how the layers of material are bonded together. Notice that most of the thickness of a fiberglass pool comes from the structure and not the thin blue decorative layer on the surface.
This cross-section illustrates the structural layers of a fiberglass pool. The grey arrow indicates the ‘osmotic’ process where pool water slowly penetrates and circulates within the gelcoat surface. This permeability exposes the layer to mineral buildup, calcium scaling, and chemical degradation.
In this image, the light blue gelcoat is breaking down revealing the brown fiberglass structure below. This pool will need to be recoated.
Adding undissolved sodium bicarbonate to the pool
If you sprinkle undissolved sodium bicarbonate (alkalinity increaser) directly into the pool, it can cause a stubborn white film to appear on the pool surface.
Prevent this white film on your pool surface by following these steps when adding sodium bicarbonate:
- Fill a bucket with pool water.
- Add the baking soda to the bucket, stirring continuously.
- Wait for the water to clear completely then pour it into the pool.
- For best results, check your pH is balanced before adding anything to the pool.
Gelcoat not cured correctly during manufacture
Defective Gelcoat
In rare instances, a fiberglass pool may turn white due to improper curing during the manufacturing process. This defect becomes apparent almost immediately—typically within the first few hours of filling the pool.
Because the uncured resin remains highly porous, water penetrates the surface and ’emulsifies’ the gelcoat, causing permanent, irreversible bleaching. If your pool maintained its original color for more than 24 hours after being filled, you can rule out a manufacturing defect. This issue is extremely uncommon; in the vast majority of cases, a white appearance is caused by topical calcium buildup rather than a gelcoat curing failure.
Stop treating your fiberglass like plaster
Did you know that water maintenance in a fiberglass pool is very different from plaster concrete (gunite) pools? Using the wrong chemical balance—a common mistake even among pool pros—can discolor your pool surface and shorten its life. Don’t let bad advice ruin your investment. Watch this video to learn the proper techniques for maintaining your pool’s surface.
Protect your pool’s appearance with our Scale & Stain Eliminator. By controlling calcium, this powerful product protects your pool surface, keeping it bright and fresh. Apply it twice a year for year-round protection.
The full calcium kit (above) removes hard calcium from the pool surface. Then, regular use of Scale & Stain Eliminator prevents it from coming back.
Frequently Asked Questions
Click headings below to see more
How can I tell the difference between calcium buildup and surface bleaching?
Calcium buildup (scale) usually feels rough or gritty to the touch, similar to fine sandpaper, and sits on top of the gelcoat. In many cases, it creates a white or greyish film that can trap dirt and algae, making the pool look discolored. Bleaching, however, is a permanent loss of color in the gelcoat itself and feels smooth to the touch. It is often caused by excessively high chlorine levels or aged surfaces.
Pro Tip: If the white area feels smooth and doesn’t change color when wet, it is likely bleaching. If it is rough and “powdery” it is likely calcium scale.
Is there any chance that the product will damage my fiberglass?
No. Our product contains no bleach, chlorine, or other bleaching agents that can strip color from a fibreglass pool surface. In fact, the formulation will not even remove the color from a T-shirt, let alone the color from a fibreglass pool surface.
Since 2019, we have used this treatment on more than 7,000 swimming pools. When used as directed, it is designed to remove staining and calcium deposits without bleaching or removing the color from the pool surface.
Most major pool manufacturers regularly suggest our product to their clients.
Why do I have a white ring at the waterline if my chemistry seems fine?
The waterline is the most common place for calcium to appear because of evaporation. When pool water evaporates at the edges, it leaves behind concentrated minerals (calcium carbonate). This process is accelerated by high heat and sunlight. Even if your overall pool chemistry is balanced, the constant “wet-dry” cycle at the tile line or gelcoat edge will eventually create a “scale line.”
Prevention: Keeping your pH on the lower end of the recommended range (7.2–7.4) and using a scale inhibitor like Scale & Stain Eliminator can help minimize this buildup.
Do I need to drain my fiberglass pool to remove heavy calcium scaling?
No, and you generally should not. Draining a fiberglass pool is risky because the structure relies on the weight of the water to counteract the “hydrostatic pressure” of the ground. Without water, the pool can buckle, crack, or even pop out of the ground.
Solution: Most calcium scaling can be treated “in-place” using our specialized chemical kits that lower the saturation index of the water, effectively forcing the water to “eat” the calcium back off the walls while the pool remains full and safe.
