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

A fibreglass pool has a smooth, non-porous gelcoat surface. Unlike plaster or concrete pool surfaces, gelcoat requires non-abrasive cleaning tools. Use soft nylon bristles, a brushed vacuum head, and a cloth for the waterline. Do not use products or equipment designed for concrete pools. They can permanently damage the gelcoat.

American product listings use the spelling “fiberglass.”

How do you clean a fibreglass pool?

Clean a fibreglass pool in the following order:

1. Skim the surface. Use a leaf net to remove floating leaves, insects, and blossoms before they sink and stain the gelcoat.
2. Brush the walls, floor, and steps. Use a soft nylon brush to remove dust and early algae growth.
3. Vacuum the floor. Move a brushed or soft-lipped vacuum head slowly across the floor in overlapping passes.
4. Wipe the waterline. Use a soft cloth or sponge and a cleaner made for pool surfaces to remove the scum line.
5. Empty the skimmer and pump baskets. Remove 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 and brush the pool about once a week, or when debris settles.

Gelcoat is non-porous. Dirt and algae adhere to it less easily than to porous plaster or concrete finishes. Brush lightly. Do not scrub.

These steps remove debris from the pool surfaces. For testing, seasonal tasks, water balance, sanitiser levels, see the fibreglass pool maintenance guide.

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

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

Do not use the following materials:

• Wire brushes
• Stainless-steel brushes
• Steel wool
• Scouring pads
• Stiff bristles

These materials can scratch the gelcoat and create rough areas where algae and stains collect. Stainless-steel brushes are intended for plaster interiors in concrete pools, not fibreglass surfaces.

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

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

Fibreglass pools can develop two types of waterline marks:

• A white, chalky ring caused by calcium buildup from 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. Use light pressure.
3. Rinse the cloth regularly.

Do not use household cleaners or bleach. These products can dull or discolour the gelcoat. If the pool is full, the products can 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. Use a sequestering product to keep calcium in the water and prevent it from 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 because its wheels can collect grit and drag it across the gelcoat.

1. Attach the vacuum head. Connect the vacuum head to a telescopic pole, then attach the vacuum hose to the head’s spigot.
2. Remove air from the hose. Lower the vacuum head to the pool floor. Slowly feed the hose into the water. Alternatively, hold the free end over a return jet. Continue until water flows from the free end and no air remains in the hose.
3. Connect the hose to the suction point. Keep the flooded end underwater and connect it to the skimmer vacuum plate or dedicated vacuum line.
4. Vacuum the pool floor. Start at the shallow end. Move the head in slow, straight, overlapping passes toward the deep end.
5. Empty the pump basket. Turn off the pump, remove debris from the basket, and restart the pump.

Manual vacuuming sends pool water through the filter. The pool size determines 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 between manual vacuuming sessions. Vacuum manually when the cleaner is unavailable or when you need to remove silt from a specific area.

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

Use the least abrasive 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

Melamine foam pads, often sold as magic erasers, remove marks through abrasion and can dull gelcoat. If you use one, apply light pressure to a single mark in a small, inconspicuous area. Do not use the pad across an entire wall.

Test all surface-cleaning products on a small area before applying them 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 that is less than half the thickness of a credit card. It protects the shell from water intrusion, algae, and chemical attack. Deep scratches cause irreversible damage. Test each cleaning method before using it on a larger area.

What must you never use to clean a fibreglass pool?

Do not use these 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.

Before choosing a treatment, identify the stain. Fibreglass pool stains can include:

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

Each stain type requires a different treatment. Do not damage or remove the gelcoat when treating a surface mark.

• Acid washing. Acid washing is for plaster and concrete pools. It works by removing a layer from these porous surfaces. Fibreglass gelcoat is a single thin coating and cannot be cleaned this way.
• Pressure washing. Pressure washing can wear away or remove the gelcoat.
• Abrasive pads and stiff brushes. Do not use steel wool, scouring pads, wire brushes, stainless-steel brushes, or stiff bristles. They can scratch the gelcoat.
• Household cleaners and bleach. These products can discolour, dull, or damage the gelcoat. They can also affect water chemistry. Use only cleaning products designed 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. Put 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 holds the shell down against groundwater. An empty or low pool shell can shift, lift, or crack. It can also damage rigid PVC plumbing. Keep the pool full. Only the builder should decide whether the pool must be drained.

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 stays on the surface. Focus on 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. An Amalfi holds 30,600 litres. Each model requires a different amount of the same product. If the water is balanced and the shock dose is correct, algae typically clears within 24 hours.

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

Do not use this process for 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 brush or soft-lipped head and a soft nylon brush. Between manual cleanings, use a suction or robotic cleaner on the pool floor. Choose equipment that does not scratch the gelcoat. Scratches can make the surface harder to clean.

Can you use CLR in a swimming pool?

No. CLR is a household descaler and is not designed for use in pool water. In a filled pool, CLR dissolves into the 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. The calcium then dries on the gelcoat.

After cleaning the residue, maintain the correct pH and use a sequestering product to reduce future buildup.

What causes brown stains on my fibreglass pool?

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

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

Identify the cause before choosing a treatment.

How do you make a fibreglass pool white again?

Identify the type of discoloration:

• A chalky white band at the waterline indicates calcium buildup.
• A grey-brown film indicates body oil and dust.
• A bleached patch indicates gelcoat damage from prolonged chlorine contact.

Cleaning removes calcium buildup, body oil, and dust. It does not restore damaged gelcoat.