How to Remove Limescale from Pool Walls

Introduction

Limescale deposits on the walls and floor of the pool are one of the most common and frustrating problems for pool owners. These white or greyish marks not only affect the aesthetics of the pool but can make surfaces rough and uncomfortable. Worse still, if left untreated, they can cause permanent damage to liners and tiles.

Limescale forms when water contains high levels of calcium carbonate and the chemical conditions favour its precipitation. This process is particularly common in regions with hard water, where minerals deposit on pool surfaces over time.

In Margem Sul, especially in areas like Palmela, Azeitão, Montijo, and Alcochete, where supply or well water is often rich in limestone, this problem is very common. In this article, we'll explain why limescale forms, how to remove it effectively, and the best strategies to prevent its recurrence.

Understanding Limescale in the Pool

What Is Limescale?

Limescale, or calcium scale, is an accumulation of calcium carbonate (CaCO₃) and other minerals on pool surfaces. It forms when:

• Water is supersaturated with calcium
• pH is elevated (above 7.6)
• Total alkalinity is high
• Water temperature is elevated
• There is significant evaporation

Types of Limescale Deposits

Signs of Limescale Problems

• White or greyish stains on walls and floor
• Surfaces rough to the touch
• Marked white line at water level
• Tiles looking dull or whitish
• Deposits in skimmers and returns

Causes of Limescale in the Pool

Unbalanced Water Chemistry

Limescale forms when the Langelier Saturation Index (LSI) is positive:

Factors contributing to positive LSI:

Hard Water

Water hardness measures the concentration of calcium and magnesium:

• Soft water: < 150 ppm calcium hardness
• Moderate water: 150-300 ppm
• Hard water: 300-400 ppm
• Very hard water: > 400 ppm

In Margem Sul, well water in Palmela, Azeitão, and areas of Montijo can exceed 400 ppm, making limescale a constant problem.

Evaporation and Concentration

When water evaporates, minerals are left behind and concentrate:

• In summer, evaporation is intense
• Replacement water adds more minerals
• Concentration increases progressively
• Deposits form more quickly

Waterline

The waterline is particularly prone to limescale because:

• It's where evaporation is most intense
• Oils and cosmetics concentrate there
• Exposure to air accelerates precipitation
• Temperature is higher at the surface

How to Remove Limescale

Initial Assessment

Before starting, assess the extent of the problem:

Light limescale:

• Thin, recent stains
• Easy to feel with hand
• Removes with mild acidic products

Moderate limescale:

• Visible deposits but not thick
• Noticeably rough surface
• Requires more intensive treatment

Severe limescale:

• Thick, hard crusts
• May need mechanical means
• May require partial or full draining

Method 1: Acid Treatment in the Water

For light to moderate limescale, without draining the pool:

Materials:

• pH reducer (dry acid or muriatic acid)
• Test kit
• Pool brush
• Circulation pump

Procedure:

1. Initial test

• Measure pH, alkalinity, and calcium hardness
• Note values for reference

1. Lower pH

• Reduce pH to 7.0-7.2
• Do it gradually, over 1-2 days
• Don't go below 7.0 to avoid damage

1. Reduce alkalinity

• If high, add acid with pump off
• This reduces alkalinity more than pH
• Goal: 80-100 ppm

1. Brush the walls

• With low pH, limescale dissolves more easily
• Brush vigorously on affected areas
• Repeat over several days

1. Maintain circulation

• Let pump run 24 hours
• Dissolved calcium disperses in water

1. Rebalance

• After 1-2 weeks, readjust pH
• Maintain between 7.2-7.4

Method 2: Direct Acid Application

For waterline and specific areas:

Materials:

• Diluted muriatic acid (1:10 with water) or commercial product
• Nylon brush or pumice stone
• Gloves and safety goggles
• Bucket

Procedure:

1. Lower water level (optional)

• Makes waterline access easier
• Allows more concentrated treatment

1. Apply acid

• Wet area with water first
• Apply acid solution with a sponge
• Let work 1-2 minutes (no more)
• Scrub with nylon brush

1. Rinse immediately

• Wash thoroughly with water
• Don't let acid dry on surface

1. Repeat if necessary

• For thick deposits, multiple applications
• Always with rinsing between them

WARNING: This method requires safety precautions. Acid can damage surfaces if applied incorrectly.

Method 3: Commercial Products

Various specific products exist for limescale removal:

Types of products:

General procedure:

1. Apply product according to instructions
2. Let work for indicated time
3. Scrub with appropriate brush
4. Rinse or let dilute in pool
5. Rebalance water chemistry

Method 4: Draining and Treatment

For severe limescale or heavily affected pools:

When necessary:

• Very thick deposits
• Limescale on entire surface
• In-water treatments didn't work
• Need to renew liner

Procedure:

1. Drain the pool

• Partial or full, as needed
• Careful with hydrostatic pressure in fibreglass pools

1. Acid treatment

• Apply diluted acid to surfaces
• Use stiff brush or pressure washer
• Work in sections

1. Rinsing

• Wash completely
• Remove all acidic water

1. Refilling

• Fill with fresh water
• Balance chemistry from the start

Useful Tools

For different levels of limescale:

• Nylon brushes: Delicate surfaces
• Stainless steel brushes: Concrete surfaces
• Pumice stone: Persistent stains (careful with vinyl)
• Plastic scrapers: Initial removal of crusts
• Pressure washer: Drained pools

Preventing Limescale

Water Chemistry Control

Prevention starts with balanced water:

Ideal parameters:

Use of Sequestrants

Metal and calcium sequestrants help prevent deposits:

• Initial dose: According to product instructions
• Maintenance dose: Weekly, reduced dose
• After filling: Always use after adding new water
• In summer: Increase frequency

Waterline Maintenance

The waterline requires special attention:

• Weekly cleaning: With sponge and appropriate product
• Level variation: Change slightly to avoid fixed mark
• Oil removal: Use specific product for grease

Well Water Management

If using well water rich in limestone:

• Test water before adding to pool
• Use sequestrant preventively
• Dilute with mains water if possible
• Consider pre-treatment for very hard water

Special Cases by Liner Type

Tiled Pools

Characteristics:

• Limescale deposits in joints and surface
• Grout can be damaged by acid
• Surface generally resistant

Treatment:

• Use acid in moderation
• Protect grout when possible
• Rinse very well

Vinyl Pools

Characteristics:

• More sensitive surface
• Don't use strong acids
• Avoid abrasives

Treatment:

• Use only products specific for vinyl
• Prefer soft brushes
• Avoid pumice stone

Fibreglass Pools

Characteristics:

• Gelcoat can be damaged
• Sensitive to prolonged low pH
• Smooth surface makes cleaning easier

Treatment:

• Mild products
• Brief treatment with low pH
• Polishing may be needed after treatment

Concrete/Plaster Pools

Characteristics:

• Porous surface absorbs limescale
• Harder to remove
• Can use more intensive treatments

Treatment:

• Muriatic acid works well
• Vigorous brushing
• May need pressure washer

Costs and Materials

Treatment Products

Professional Treatment

For severe cases:

• Assessment and treatment: €150-300
• Draining and complete treatment: €300-600
• Liner renovation: €1000-5000+

Related Problems

Limescale in Equipment

Limescale also affects:

• Heaters: Reduces efficiency, can damage
• Pumps: Premature wear
• Filters: Partial blockage
• Salt cells: Reduces chlorine production

Prevention:

• Keep chemistry balanced
• Use sequestrants regularly
• Do preventive maintenance

Combination of Limescale and Other Problems

Limescale can combine with:

• Metals: Creates coloured deposits
• Algae: Limescale gives texture for algae to attach
• Dirt: More visible marks

Specific Zones in Margem Sul

Palmela and Azeitão

• Very chalky spring water
• We recommend sequestrant as routine
• Test water hardness regularly
• Consider softening system

Montijo and Alcochete

• Variable well water
• Test before each filling
• Use pre-treatment if necessary

Coastal Zones

• Fewer limescale problems
• More attention to sea spray
• Combination of salt and limescale possible

Frequently Asked Questions

Does limescale damage the pool?

Yes, in the long term. Limescale makes surfaces rough, can damage grout, and creates a surface where algae attach more easily. In equipment, it can cause failures and reduce efficiency.

Can I swim with limescale in the pool?

Yes, limescale itself isn't dangerous to health. However, rough surfaces can be uncomfortable and the water chemistry causing limescale may not be ideal.

How long does it take to remove limescale?

Depends on severity. Light limescale can be treated in 1-2 weeks with low pH and brushing. Severe deposits may require professional treatment or draining.

Does limescale come back?

If you don't correct the cause, yes. Prevention through balanced chemistry and use of sequestrants is essential to avoid recurrence.

Can I use vinegar to remove limescale?

Vinegar (acetic acid) works for light stains, but is too weak for significant deposits. Specific products or diluted muriatic acid are more effective.

Conclusion

Limescale on pool walls is a common problem, especially in regions with hard water like Margem Sul. Key points for solving and preventing this problem are:

• Identify the cause – usually high pH, high alkalinity, or hard water
• Choose the appropriate method – from in-water treatment to draining
• Use safety products – acids require protection
• Prevent recurrence – maintain balanced chemistry and use sequestrants
• Regular maintenance – especially of the waterline

If you need professional help with your pool in Margem Sul, ManutençãoPiscinas is here to help. Contact us for a no-obligation quote.