How to Clean a Pool: Fibreglass Steps, Tools & Stains

A fibreglass pool has a smooth, non-porous gelcoat surface. This differs from the porous plaster or concrete used in concrete pools. To protect the gelcoat, use soft nylon bristles, a brushed vacuum head, and a cloth for the waterline. Do not use products or equipment designed for concrete pools, as they can permanently damage the gelcoat. Fibreglass is spelled fiberglass in American product listings.

How do you clean a fibreglass pool?

Clean a fibreglass pool in this order:

1. Skim the surface. Use a leaf net to remove floating leaves, insects, and blossom before they sink and stain the gelcoat.
2. Brush the walls, floor, and steps. Use a soft nylon brush to remove settled dust and early algae growth.
3. Vacuum the floor. Move a brushed or soft-lipped vacuum head across the floor using slow, overlapping passes.
4. Wipe the waterline. Use a soft cloth or sponge with a cleaner made for pool surfaces to remove the scum line.
5. Empty the skimmer and pump baskets. Remove any collected debris from both baskets.

Skim surface debris daily, especially during leaf-fall season. Summer storms in South East Queensland can deposit leaf litter and phosphate into an open pool in one afternoon. Vacuum the floor about once a week or whenever debris settles. Brush the pool during the same weekly cleaning.

Gelcoat is non-porous, so dirt and algae do not adhere to it as easily as they do to porous plaster or concrete finishes. Use light brushing rather than scrubbing.

Skimming, brushing, and vacuuming remove debris from the pool surface. Water balance, sanitiser levels, testing, and seasonal tasks are covered in fibreglass pool maintenance.

What do you use to brush the walls and floor of a fibreglass pool?

Use a pool brush with soft nylon bristles. Attach it to a telescopic pole to clean the walls, floor, and steps. It removes settled dust, pollen, and early algae film without scratching the gelcoat.

Do not use wire brushes, stainless-steel brushes, steel wool, scouring pads, or stiff bristles. These materials can scratch the gelcoat. Scratches create rough areas where algae and stains can collect. Stainless-steel brushes are designed for plaster interiors in concrete pools, not fibreglass surfaces.

Brush the pool during weekly vacuuming. Brush it again after a storm or heavy use.

How do you clean the waterline and scum line on a fibreglass pool?

A fibreglass pool can develop two types of waterline marks:

• A white, chalky ring caused by calcium concentrated by heat and evaporation.
• A grey-brown, greasy ring caused by body oils, sunscreen, and airborne dust.

To remove an oily scum line:

1. Apply a cleaner designed for pool surfaces.
2. Wipe the area with a soft cloth or sponge using light pressure.
3. Rinse the cloth regularly.

Do not use household cleaners or bleach. These products can dull or discolour the gelcoat. In a full pool, they also enter the swimming water.

Calcium deposits require water chemistry management. Scrubbing removes the existing deposit but does not prevent it from returning. Keep the pH between 7.2 and 7.4 and use a sequestering product to keep calcium in the water instead of depositing at the waterline.

How do you vacuum a fibreglass pool by hand?

Use a brushed or soft-lipped vacuum head. Do not use a wheeled vacuum head. Wheels can collect grit and move it across the gelcoat.

1. Fit the head to the pole and hose. Attach the vacuum head to a telescopic pole. Push the vacuum hose onto the head's spigot.
2. Remove air from the hose. Lower the vacuum head to the pool floor and slowly feed the hose into the water. Alternatively, hold the free end over a return jet. Continue until water runs from the far end and no air remains in the hose.
3. Connect the hose to the suction point. Keep the flooded end under water and connect it to the skimmer vacuum plate or dedicated vacuum line.
4. Vacuum in slow, overlapping passes. Start at the shallow end. Move the head in straight, slow strokes toward the deep end. Overlap each pass.
5. Empty the pump basket. Turn off the pump, remove debris from the basket, and restart the pump.

Hand vacuuming sends pool water through the filter. Pool size affects how long vacuuming takes and how much water passes through the filter. An Empire holds 18,700 litres. An Amalfi holds 30,600 litres.

Use a suction cleaner or robotic cleaner to clean the floor between manual vacuuming sessions. Vacuum by hand if the cleaner is unavailable or to remove silt from a specific area.

What can you use on a stubborn mark without damaging the gelcoat?

Use the softest tool that removes the mark. Test it on a small, hidden area first.

Safe options include:

• A soft nylon brush
• A soft cloth or sponge
• A cleaner formulated for pool surfaces

Do not assume that a melamine foam pad, often sold as a magic eraser, is safe for gelcoat. It removes marks by abrasion and can dull the gelcoat. If you use one, apply light pressure to a single mark in a small, inconspicuous area. Do not use it across an entire wall.

Test any surface-cleaning product on a small area before applying it to a visible surface.

Do not use a pumice stone on a fibreglass pool. Pumice is intended for tile and concrete and will scratch gelcoat.

Gelcoat is a thin surface layer, less than half the thickness of a credit card. It protects the shell against water intrusion, algae, and chemical attack. Deep scratches cause irreversible damage, so always test cleaning methods before using them on a larger area.

What must you never use to clean a fibreglass pool?

Do not use the following methods to clean a fibreglass pool:

• Acid washing
• Pressure washing
• Abrasive pads or stiff brushes
• Household cleaners or bleach
• Undissolved chlorine placed against the surface
• Draining the pool

MFP Easy installs more than 250 fibreglass pools each year across South East Queensland. These restrictions are based on that work.

Identify the type of stain before selecting a treatment. Fibreglass pool stains can include:

• Organic stains from leaf litter
• Metal stains from iron, copper, or manganese in fill water
• Calcium deposits

Each type requires a different treatment. Do not remove or damage the gelcoat to treat a surface mark.

• Acid washing. Acid washing is intended for plaster and concrete pools. These porous surfaces can be treated by removing a surface layer. Fibreglass gelcoat is a single thin coating and cannot be treated this way.
• Pressure washing. Pressure washing can strip and wear the gelcoat, removing the shell’s protective layer.
• Abrasive pads and stiff brushes. Do not use steel wool, scouring pads, wire brushes, stainless-steel brushes, or stiff bristles. These products scratch gelcoat.
• Household cleaners and bleach. These products can discolour, dull, or damage gelcoat. They can also affect water chemistry. Use only cleaning products made for pool surfaces.
• Undissolved chlorine held against the surface. Chlorine tablets and cal-hypo or dichlor granules can bleach, blister, or damage the resin surface when left against the gelcoat. Keep chlorine tablets in a floating dispenser or skimmer basket. Do not leave tablets or granular chlorine on the pool floor. Very high free chlorine levels can permanently bleach the surface.
• Draining the pool. Do not empty a fibreglass pool for cleaning. The water inside the pool holds the shell down against groundwater. An empty or low shell can shift, lift, or crack and can damage rigid PVC plumbing. Keep the pool full. Only the builder should decide whether draining is required.

How do you get algae out of a fibreglass pool?

Follow these steps:

1. Brush the entire pool shell with a soft nylon brush.
2. Balance the water and add a standard chlorine shock.
3. Run the filtration system for at least 24 hours.

Brush the pool before adding chemicals. On a gelcoat shell, algae remains on the surface rather than becoming embedded in it. Pay particular attention to corners, steps, and the wall below the returns, where water circulation is slower. Check these areas again after the water clears.

Calculate the shock dose based on the pool’s water volume. A Bellagio holds 19,500 litres, while an Amalfi holds 30,600 litres. The required amount of the same product differs between these models. When the water is balanced and the shock is dosed correctly, algae typically clears within 24 hours.

After adding the shock, run the filtration system for at least 24 hours. This circulates chlorine through the pool and moves dead algae into the filter.

This process does not apply to black spotting. Diagnose black spotting before adding more chemicals.

FAQs

What is the best pool cleaner for a fibreglass pool?

For routine cleaning, use a manual vacuum with a brushed or soft-lipped head and a soft nylon brush. Between manual cleanings, use a suction or robotic cleaner for the pool floor. Choose equipment that does not scratch the gelcoat, as scratches make the surface harder to clean.

Can you use CLR in a swimming pool?

No. CLR is a household descaler and is not formulated for use in pool water. Because the pool remains full during cleaning, the descaler dissolves into the pool water instead of rinsing down a drain. To remove calcium at the waterline, adjust the pH and use a product designed for pool surfaces.

What is the white chalky residue on my fibreglass pool?

The white residue at the waterline is calcium buildup. Heat and evaporation concentrate calcium at the waterline, where it dries on the gelcoat. After cleaning, control the pH and use a sequestering product to prevent the buildup from returning.

What causes brown stains on my fibreglass pool?

Brown stains on a fibreglass pool usually have one of two causes:

• Organic material: Leaves and debris left on the pool floor or in a corner.
• Metals: Iron, copper, or manganese in the fill water.

Identify the cause before selecting a treatment.

How do you make a fibreglass pool white again?

Identify the type of discoloration before cleaning:

• A chalky white band at the waterline is calcium buildup.
• A grey-brown film is body oil and dust.
• A bleached patch is gelcoat damaged by prolonged contact with chlorine.

Cleaning can remove calcium buildup, body oil, and dust. It cannot restore the colour of damaged gelcoat.