Closing a Fiberglass Pool: The Complete Step Checklist

Closing a fiberglass pool takes nine ordered steps. Start by balancing your water chemistry: buffer alkalinity to 80, 120 ppm, fine-tune pH to 7.2, 7.4, then verify calcium hardness below 120 ppm. Next, skim, brush, and vacuum. Clean your filter, store accessories dry, and remove the salt cell. Winterize plumbing with blowouts, plugs, and pool-grade antifreeze. Shut down power, then cover and anchor. Miss one step, and you’ll face cracked pipes or spring surprises worth avoiding.

Key Takeaways

• Balance water chemistry in order: buffer alkalinity to 80, 120 ppm, adjust pH to 7.2, 7.4, then verify calcium hardness below 120 ppm.
• Clean the pool thoroughly by skimming the surface, brushing walls and corners, then vacuuming the floor with overlapping passes.
• Clean and drain the filter, then fully drain the pump, heater, and chlorinator so standing water cannot freeze and crack housings.
• Blow out plumbing lines until bubbles emerge, install expansion or Gizzmo plugs, and add pool-grade antifreeze, never automotive antifreeze.
• Remove, clean, and store the salt cell indoors, then cut all power, pull fuses, and secure the pool cover.

Balance Your Fiberglass Pool Water Chemistry

Balance your fiberglass pool water chemistry to protect the surface through winter. Water chemistry balancing is a critical first step when closing a fiberglass pool. Start by adjusting the pH to a range between 7.2 and 7.4. Next, set total alkalinity to 80, 120 ppm for maximum stability. Keep calcium hardness below 120 ppm, since fiberglass surfaces require lower levels than other pool types. Add a chelating agent or a stain and scale remover, following the product instructions precisely. If chlorine levels run low, use liquid chlorine or a nonchlorine shock instead of Cal-Hypo. Getting these parameters right when winterizing your fiberglass pool prevents staining, scaling, and surface damage while the pool sits closed through the cold months.

Dial In pH, Alkalinity, and Calcium Hardness

Dial in pH, alkalinity, and calcium hardness by hitting three specific targets in the correct order. During fiberglass pool closing, sequence matters because alkalinity buffers pH, so you’ll stabilize it first, then fine-tune pH, and verify hardness last. Work through these values as part of your pool closing checklist:

Sequence is everything: buffer alkalinity first, fine-tune pH next, and verify calcium hardness last for a protected fiberglass shell.

1. Adjust total alkalinity to 80, 120 ppm for ideal buffering stability.
2. Set pH between 7.2 and 7.4 before you seal the pool.
3. Confirm calcium hardness stays below 120 ppm, the fiberglass-specific ceiling.
4. Add a chelating agent or stain and scale remover per product instructions.

Retest after each adjustment, since one change shifts another. Precise numbers protect the shell and prevent staining through months of dormancy.

Skim, Brush, and Vacuum the Pool

Skim, brush, then vacuum the pool in that deliberate order. Start by skimming the surface to remove all leaves, twigs, and floating debris before they sink. Next, clean the water line and brush the walls, steps, and corners to loosen algae and dislodge buildup that clings to the fiberglass. Work systematically from the shallow end toward the deep end so suspended particles settle in one direction. Finally, vacuum the pool floor thoroughly, moving slowly to capture the dirt and debris you’ve just brushed free. Overlap each pass to avoid missing sections. Completing these steps in sequence prevents recontamination and ensures the shell stays clean throughout the closure, reducing staining and algae growth over winter.

Clean the Filter Before You Close

Before you close, clean your filter to prevent contaminants from settling over the off-season. If you’re running a sand or DE system, backwash the filter until the sight glass runs clear; for cartridge systems, remove and hose down each cartridge thoroughly. Once cleaned, prep the filter for storage by draining residual water so it’s ready for winter.

Backwash the Filter

Backwash the filter to clear trapped debris and contaminants before you seal the pool for the season. This process reverses water flow through the filter media, flushing accumulated dirt out through the waste line. Complete this step before draining equipment and expelling plumbing lines.

Follow this sequence to backwash correctly:

1. Turn off the pump and set the multiport valve to the “Backwash” position.
2. Restart the pump and run it until the sight glass shows clear water, typically two to three minutes.
3. Turn off the pump, switch the valve to “Rinse,” and run for thirty seconds.
4. Shut down the pump and return the valve to “Filter.”

Confirm the pressure gauge reads normal before proceeding to equipment drainage.

Clean the Cartridge

Clean the cartridge by turning off the pump and shutting down power to the equipment. If your pool uses a cartridge filter instead of a sand system, you’ll clean the cartridge rather than backwash it. Release the air relief valve, then open the filter housing and remove the cartridge. Inspect the pleats for tears, cracks, or embedded debris. Spray the cartridge with a garden hose, working top to bottom and separating each pleat to flush out trapped dirt. For oils or heavy buildup, soak the cartridge in a filter-cleaning solution per the product instructions, then rinse thoroughly. Let the cartridge dry completely before storing it in a dry location for winter. Reassemble the housing only if you’re leaving the cartridge in place through the off-season.

Prep for Storage

Prep for storage by flushing your filter completely before winter to prevent trapped debris and organic buildup from hardening over the off-season. Backwash the filter or remove and clean the cartridge until the water runs clear. After rinsing it, prep the entire system for cold-weather storage by draining every component and isolating removable parts.

1. Disconnect and drain pumps, filters, heaters, and chlorinators completely.
2. Drain the pump housing and store the drain plug separately to avoid loss.
3. Remove salt system cells, clean them with Salt Cell Saver, and store in a dry location.
4. Turn off all power, then remove fuses or switch circuit breakers to “off”.

Store cleaned components indoors, fully dry, to prevent corrosion, cracking, and residual moisture from freezing inside sensitive equipment.

Store Toys, Floats, and Accessories

Store all pool toys, floats, rafts, and accessories in a dry, protected location shielded from freezing temperatures and UV exposure. Round up every item from the water, deck, and surrounding area so nothing’s left exposed to winter conditions. Wash each piece thoroughly to remove dirt, algae, and residual chemicals that can degrade materials over time. Rinse them clean, then let them dry completely to prevent mold and mildew during storage. Deflate all inflatable floats and rafts, pressing out trapped air to reduce their footprint and avoid stress on seams. Keeping accessories clean, dry, and properly deflated extends their lifespan and ensures they’re ready for reuse when you reopen the pool next season.

Drain the Pump, Filter, and Heater

Drain the pump, filter, heater, and chlorinator completely by disconnecting each unit and expelling all standing water. Standing water inside any component will freeze, expand, and crack housings, so full expulsion is critical. Work through each unit methodically:

1. Disconnect and drain the pump, then remove the drain plug and store it separately to avoid loss.
2. Drain the filter fully, backwashing sand or rinsing the cartridge beforehand.
3. Open the heater’s drain valves and clear all residual water from the heat exchanger.
4. Drain the chlorinator, removing any remaining tablets or chemical residue.

Confirm every plug and valve is open and each component sits empty. Store removed plugs together in a labeled container so reassembly next season stays straightforward.

Blow Out the Plumbing Lines

Blow out the plumbing lines using a shop vac or air compressor to expel all standing water from the lines that connect the pool to the pump and filter system. Continue blowing until bubbles emerge from the pool’s jets and returns, confirming each line’s fully cleared. After you’ve verified clearance, insert expansion plugs or Gizzmo plugs rated for your specific pipe diameter into all lines. This creates a tight seal and accommodates any pressure changes during freezing. For added protection, add pool antifreeze to the lines to prevent freezing of any residual water that remains after blowing out. Don’t skip this step in cold climates, since trapped water can crack fittings, pipes, and equipment over winter.

Plug and Antifreeze Your Pipes

Once you’ve blown out the plumbing, drain and clear any remaining water from the lines to confirm they’re empty. Insert winterizing plugs or Gizzmo plugs rated for your pipe diameter into all lines and returns. Then add pool antifreeze to each line to protect against freezing from any residual water.

Drain and Clear Lines

Clear every line completely before sealing the pool, because standing water in your plumbing can freeze and crack pipes over winter. Start by removing all plugs from the pump and filter system, then drain the standing water. Use a shop vac or air compressor to force water out of each line until you confirm complete clearance.

1. Remove all plugs and drain the pump and filter system.
2. Blow out plumbing lines with a shop vac or air compressor.
3. Continue until bubbles emerge from the pool jets and returns.
4. Confirm every line reads clear before proceeding.

Once bubbles appear consistently, you’ve expelled the standing water and can move on to plugging and adding antifreeze to protect against any residual moisture.

Install Winterizing Plugs

Insert expansion plugs or Gizzmo plugs rated for your specific pipe diameter into all lines. Match each plug to its port and tighten until the rubber gasket expands fully against the pipe walls, creating a watertight seal. This prevents any incoming water from entering the plumbing during winter. After you’ve cleared the lines, seal them to block any residual water from refreezing and cracking your pipes.

Next, add pool antifreeze to the lines to protect against freezing of any residual water the blowout didn’t clear. Pour the antifreeze directly into each line according to the product’s instructions, using only pool-rated antifreeze, never automotive antifreeze, which is toxic. This combination of mechanical plugs and antifreeze gives your fiberglass pool’s plumbing complete freeze protection through the cold months.

Add Pool Antifreeze

Add pool antifreeze to guard against any water the blowout left behind. Even after a thorough line clearance, trace moisture can pool in low spots and freeze, cracking pipes over winter. Pool antifreeze fills that gap, protecting residual water in your plumbing.

1. Confirm you’re using pool-grade antifreeze only, never automotive antifreeze, which is toxic and unsafe for pool systems.
2. Pour antifreeze directly into each line per the product’s dosage instructions.
3. Distribute it across all lines, including skimmer and return runs, to cover every vulnerable section.
4. Verify plugs remain seated so antifreeze stays contained within the plumbing.

With your lines protected, you’re ready to move on to equipment drainage and storage.

Remove and Store the Salt Cell

Remove the salt system cell from your plumbing before winter sets in, since residual water inside can freeze and crack the housing. Disconnect the cell’s unions on both ends and detach any wiring connections. Inspect the interior plates for scale buildup. Clean the cell with Salt Cell Saver, following the product’s dilution instructions to dissolve calcium deposits without damaging the plate coating. Rinse thoroughly and let the cell dry completely to prevent moisture retention. Store the cell in a dry, temperature-controlled location away from direct sunlight and freezing conditions. Cap the open plumbing ends or insert dummy cells to seal the line. Keep the cell’s fittings and hardware together so you won’t lose components during reassembly when you reopen the pool.

Shut Down Power to All Equipment

Shut down power to all equipment by cutting power to everything before you finish closing the pool. Removing electrical supply prevents accidental startup and protects components through the off-season. Work methodically through each connection point to confirm total shutdown.

1. Turn off all power to support equipment at the main switch.
2. Remove fuses from the equipment panel to eliminate residual current.
3. Switch circuit breakers to the “off” position for pumps, heaters, and chlorinators.
4. Verify each device is de-energized before leaving the area.

Don’t skip verification. A single live circuit can damage drained equipment or create a hazard during winter storage. Once you’ve confirmed every component is powered down, you’re ready to move on to lowering the water level.

How Low Should Fiberglass Pool Water Go?

Fiberglass pool water should go no lower than the bottom of the skimmer. For fiberglass-specific needs, aim for a level 2, 4 inches below the skimmer opening. Never fully drain the pool, since removing all water risks the shell pulling away from the ground and structural damage.

If you’re installing a solid cover without a pump, lower the water 6 inches below the return jets to accommodate accumulation. When cover fit requires it, bring the water back up to 4 inches below the skimmer.

Measure precisely as you drain, and stop once you hit your target range. Overdraining a fiberglass shell creates costly problems, so monitor the level throughout the process.

Install and Secure Your Winter Cover

Install and secure your winter cover by draping it across the pool so it extends 3, 4 feet beyond the edge on all sides. This overhang guarantees full coverage and secure anchoring. Once positioned, work methodically through the following steps:

1. Smooth out all wrinkles so the cover lies flat against the water surface, eliminating gaps where debris collects.
2. Anchor the cover with water bags filled three-quarters full, allowing room for expansion during freezing temperatures.
3. Deploy deck anchors or a cover pump to prevent water accumulation on solid covers.
4. Seal the cover edge completely to stop wind from getting underneath the material.

Verify each anchor point holds firm before you finish. A properly secured cover protects your fiberglass shell throughout the off-season and simplifies spring reopening.

Conclusion: Closing Your Fiberglass Pool the Right Way

Closing a fiberglass pool properly protects it through the off-season and makes spring opening much easier. The key steps are balancing the water, lowering the level as needed, blowing out and plugging the lines, adding winter chemicals, and securing a good cover. Fiberglass pools are forgiving, but skipping steps like winterizing the plumbing can lead to freeze damage. A careful close, or a professional one, keeps the pool in great shape until you reopen it.

Get Expert Pool Construction & Care

Fiberglass pool ownership becomes easier when you start with quality construction and expert guidance from day one. At Schiller Pools in Jupiter, FL, our experienced team provides trusted Pool Construction with premium craftsmanship and 40+ years of Florida experience. Call +1 (561) 475-5997 today and get your free estimate.

Frequently Asked Questions

When Is the Best Time of Year to Close a Fiberglass Pool?

Most people close in fall once the water cools and swim season ends, often when temperatures drop into the 60s and stay there. Closing before a hard freeze is important in cold climates to protect the plumbing. Waiting until the water is consistently cool also helps prevent algae over the winter.

How Much Does Professional Pool Closing Typically Cost?

Professional closings are usually a flat service fee that varies by region, pool size, and what is included, such as winter chemicals or a cover. It is generally an affordable seasonal cost. A local pool company can quote your pool, and booking opening and closing together sometimes earns a discount.

Can I Close My Fiberglass Pool Without Any Professional Help?

Many owners close their own pool if they are comfortable with the steps: balancing the water, lowering the level, blowing out and plugging the lines, adding winterizing chemicals, and covering it. The plumbing is the part where mistakes cause freeze damage, so if you are unsure there, a professional close is worth it.

How Often Should I Check on My Pool During Winter?

Checking every few weeks is a good habit. Look that the cover is secure and clear of heavy water or debris, and that the water level and chemistry are holding. In stormy or very cold spells, check more often. Catching a slipped cover or a dropping water level early prevents bigger problems by spring.

What Tools Do I Need to Close a Fiberglass Pool?

A typical close needs a water test kit and winterizing chemicals, a way to lower the water, an air blower or shop vac to clear the lines, plugs for the openings, and a winter cover. A skimmer and brush help with a final clean. Your pool’s manual lists anything specific to its equipment.