Calcium buildup in pool
How to remove calcium buildup in pool
Rough white calcium deposits can make even a beautiful swimming pool look old, dirty, and neglected. Unfortunately, calcium buildup is one of the most difficult pool problems to remove — especially when it forms thick scale or hard calcium nodules.
The good news is that most calcium buildup can be removed without draining the pool or acid washing the surface.
We specialize in removing calcium deposits from plaster, pebbletec, quartz, tiled, and fiberglass pools safely and effectively.
Calcium Buildup - Quick facts
- Usually caused by high pH and high calcium hardness
- Very common in new plaster pools
- Often appears as rough white spots or scale
- Acid washing removes it but damages the surface
- Calcium spots will often attract algae and dirt
- Calcium can be removed without draining or acid washing
Calcium scale is more than just an eyesore—it’s a rough, sandpaper-like deposit that clings to your pool’s walls, floors, and waterline. Typically appearing as white or grey patches, this buildup creates a “gritty” layer that acts like a magnet for dirt and algae, making your pool harder to clean and maintain.
Remove calcium scale without draining or acid washing
We strongly advise against acid washing. While an acid wash might be a temporary fix, it is inherently destructive. Acid washing etches and dissolves the pool finish, creating a more porous and rough surface where calcium can easily start forming again. Also, without treating the water with a dedicated calcium preventative, you’re often left with the same buildup within months. We focus on long term solutions that protect the surface, not strip it away.
Don’t drain your pool to remove hard calcium deposits. Our treatments remove calcium buildup in pool surfaces, including Plaster, Quartz, Pebbletec, and fiberglass pools. And, we include a long-lasting prevention polymer to help stop calcium from coming back later.
Our calcium removal kit is a better and more affordable alternative to acid washing. Learn more about acid washing here. If you’re unsure about the type or cause of your calcium, please contact us—we’re happy to help.
Calcium Scale Removal Options
Calcium Scale Removal DIY kit
- (64oz) of our calcium prevention formula
- 9 lbs of our calcium dissolving compound
- Phone support from our technicians
- Simple step-by-step instructions included
- Pool does NOT need to be drained
- Kit is sent express and tracked by UPS
- Kids are back in the pool in just 7 days
- The kit is $295 for pools larger than 12,000 gallons
Calcium Scale Removal –
On Site Technician
- (64oz) of our calcium prevention formula
- 9 lbs of our calcium dissolving compound
- Complete 7 point water test
- Your pool does NOT need to be drained
- Kids are back in the pool in 7 days
- Visit is $405 for pools over 12,000 gallons
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What causes calcium buildup
Scale forms when calcium precipitates out of your pool water and bonds to the surface. Several factors contribute to calcium formation including:
- Imbalanced Chemistry: High pH, total alkalinity, or calcium hardness levels.
- Water Source: Using hard (calcium rich) water or well water to fill the pool.
- Environmental Factors: Warm water and high evaporation rates.
- Calcium-based Chlorine: ‘Cal-Hypo’ contains around 30% calcium which raises the calcium level in your pool.
As a general rule, high pH is the main reason why calcium bonds to pool surfaces. In most cases, calcium issues are greatly reduced with pH management and the regular use of Scale & Stain Eliminator. which uses polymers to help stop calcium for precipitating onto the surface. By the way, if you are in a constant battle with high pH, this blog post about boric acid may help to better regulate pH fluctuations.
Poor surface application causes calcium nodules
When a new plaster or pebble surface is applied to a new or remodeled pool, poor plaster application can leave air bubbles or voids. These voids fill with water, which then calcifies. Then, as the calcium in the void continues to grow over time, it forces its way out through the interior and forms a visible calcium lump on the pool surface. This white lump (often looks like an icicle) is called a calcium nodule.
The most common trait of calcium nodules is that after they are rubbed away, they often regrow in the same place a few weeks later.
Pool interiors use calcium rich white cement
Most light-colored pool surfaces use white cement instead of traditional grey cement to achieve a brighter appearance. However, white cement contains around 36% calcium hydroxide. This calcium-rich cement cures (hydrates) and releases calcium into the pool water, which increases the risk of calcium issues. This leads to the formation of a thin calcium layer that keeps growing, attracting more calcium and eventually forming larger, widespread deposits.
If you see calcium buildup in your pool, it’s important to take action now. If left untreated, calcium deposits can lift, crack, and break apart your pool surface, leading to severe and costly damage. Unfortunately, we often see pools with extensive surface destruction caused by huge calcium spots that could have been prevented.
If you are dealing with calcium buildup on a fiberglass pool surface, visit our page on removing calcium from fiberglass pools here.
Calcium Scale on new pool plaster
When fresh plaster is applied, it goes through a curing process that releases calcium hydroxide into the water. The new plaster/pebble floods the pool water with calcium and constantly raises the pH.
This combination is the perfect storm. High pH reduces the water’s ability to suspend calcium, and with calcium being added during the curing process, the water often becomes over-saturated. Then, the water deposits the calcium carbonate on the pool surface.
Without careful water balancing in the first few weeks, scale can form and become difficult to remove. Staying on top of pH, alkalinity, and calcium hardness from day one is vital.
To protect your investment, the consistent use of Scale & Stain Eliminator. helps stop calcium formation and keeps your surface smooth and blue.
Frequently Asked Questions
Click headings below to reveal more information
How can I tell if my pool stain is actually calcium?
Calcium stains (scale) typically appear as white or light grey/brown deposits that are rough and gritty to the touch, like rough sandpaper. Calcium often forms a white crust along the waterline, “lumps” on the floor, or icicle-like growths known as nodules on the pool walls. Calcium can also make the surface look ‘blotchy’ and discolored in patches of the pool.
The Acid Test: You can confirm it is calcium by placing a drop of diluted muriatic acid on the deposit at the waterline. If it fizzes, it is calcium carbonate. If it does not react but is still hard and white, it is likely the more stubborn calcium silicate. As a rule, if you have a hard white buildup under the water that will not brush away then it is almost certainly some form of calcium.
Can calcium stains turn different colors, like brown or gray?
Yes. While very porous. As the scale grows, it acts like a magnet, trapping dirt, minerals (iron or copper), and algae within its structure. This can cause the calcium to appear brown, green, or grey.
Note: These “colored” stains often cannot be removed by traditional brushing or chlorine because the calcium film acts as a “shield,” protecting the trapped dirt and metals from cleaning chemicals. You must first dissolve the calcium layer to reach the underlying stain. Our calcium treatment kit dissolves calcium and also has a prevention polymer to stop it from coming back.
If I remove the calcium, won't it just come back again?
No you can keep the calcium away for good if you do the following:
- Keep the water balanced – ensuring that the pH, alkalinity and Calcium Hardness (or total hardness) are all within the suggested ranges.
- Brush the pool surface once a month – Doing this will help remove soft calcium that is trying to take hold on the surface of the pool.
- Use Scale and Stain Eliminator – in your pool every 6 months. This advanced polymer works actively to keep calcium in a liquid state and helps prevent it from ‘plating out’ onto the pool surface.
- Avoid calcium based granular chlorine – Calcium hypochlorite is a common ingredient in granular chlorine and can cause elevated calcium levels in the pool which can lead to scale formation.
Following these steps will help keep the calcium away and keep your surface looking great. Also, the surface will remain smooth on hands and feet and be a plesure to swim in for many years to come.
What are "calcium nodules" and why do they keep coming back?
Calcium nodules look like small white volcanoes or icicles growing out of the pool walls or floor. They are often caused by “voids” or air bubbles trapped beneath the plaster during the pool’s construction or remodeling. Water seeps into these voids, reacts with the calcium-rich cement, and is forced back out through the surface, creating a lump (nodule).
Warning: If you scrape a nodule off and it reappears in the same spot a month or so later, it likely indicates a de-lamination (a section of the surface has separated from the main structure). This is very common and these nodules can be removed with our calcium treatment Kit.
Why is my new plaster pool developing scale so quickly?
New pool surfaces are highly susceptible to scaling because of the “curing” process. Light-colored pool interiors use white cement, which is roughly 36% calcium hydroxide. As this cement hydrates, it releases calcium into the water.
This is why a proper “start-up” process is vital. If the pH is not strictly controlled during the first few months, the released calcium will immediately bond to the new surface, creating a thin, hazy film that highlights imperfections and makes the pool look dull. Our Scale and Stain Eliminator liquid helps keep the calcium in a liquid state and keeps the surface clean. It is also important to brush the surface and test the water every 2-3 days during the first few months.
What does calcium look like in swimming pools?
Hard white balls/spots
These spots are about the size of a small ball bearing (approx. 1/8-1/4 inch n diameter) that bond randomly over the walls and floor of your pool and won’t brush away. These are referred to as calcium nodules. These occur when a void of calcium-rich water under the pool surface pushes calcium into the pool. These nodules form because of poor surface installation. See diagram.
White calcium nodules (iciles)
Nodules are approx. 1/4 inch wide and 1-3 inches long and can appear to be ‘growing’ out of the walls or floor of your pool. This type of formation indicates that a section of the pool surface has de-laminated (pushed out) from the main pool structure. If the calcium spot reappears in the same place after cleaning, de-lamination 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.
Course Brown Stains
When dirt or metals are captured by precipitated calcium, it will leave a dirty colored brown stain that will not brush away. Sometimes this dirt contamination can also turn calcium lumps a light brown rather than white.
In some cases, calcium can appear in the form of a thin calcium film that covers dirt or metal stains on the pool interior. This type of staining cannot be removed with brushing or chlorine because the calcium film ‘shields’ the staining from your pool brush.
White calcium blotches on the pool surface
When you see swirl marks or weird patterns on the bottom of your pool it is usually because calcium has started to precipitate. When this happens, it leaves a light white film on the surface that highlights the imperfections in the pool surface.
Some clients say that their pool looked great at first, but later on, they now see swirl marks from troweling, footprints, ridges, or trowel marks that have appeared a short time later.
For more in-depth scientific information about calcium formation click here.
Warm water makes calcium more likely
Most substances dissolve better and faster in hot water, but calcium is an oddball. Calcium becomes less soluble (more likely to plate out) as water gets warmer. Instead of staying dissolved, it turns into a solid crust and “plates out” on the pool surface. So, if you are turning on your heater for the season, check the pH because high pH and warm water are perfect conditions for calcium formation.
Pool heater pipes trap calcium
While your pool water might feel warm, the water inside the heater reaches very high temperatures up to 400°F. This heat forces the calcium to crystallize, coating the internal pipes in a hard calcium scale. This buildup acts like insulation, making your heater less efficient, consume more power and eventually causing it to overheat or fail. Just another reason why water maintenance and using scale and stain eliminator regularly is so important.
