How To Close an In-Ground Fiberglass Pool
Closing your fiberglass pool correctly before winter is one of the most important steps in maintaining your investment. A properly winterized pool prevents damage from freezing, protects plumbing and equipment, and makes spring opening fast and easy. Follow these professional steps from Mock Pools & Ponds to safely close your in-ground fiberglass pool.
Why You Should Never Skip Pool Closing
When winter temperatures drop, even a small amount of standing water can expand, crack fittings, and damage pumps or filters. Fiberglass pools, in particular, should never be drained completely — doing so can cause the shell to lift or shift due to groundwater pressure. Proper pool closing protects your structure, surface, and plumbing system all winter long.
Before You Begin
- Never fully drain a fiberglass pool. Always leave enough water to support the shell and prevent floating or warping.
- Lower the water level only if necessary. For most fiberglass pools, you can leave water at its normal level by using return plugs and a skimmer gizmo.
- Balance your pool chemistry. Correct pH and alkalinity levels help prevent stains, corrosion, and algae while the pool is closed.
- Work safely. Wear gloves and goggles when handling pool chemicals and never mix chlorine with acids or algaecides.
Pool Closing Tools and Supplies
- Pool brush, vacuum, or robotic cleaner
- Water test kit or professional water analysis from Mock Pools & Ponds
- Air blower, shop vac, or compressor for blowing out lines
- Winterizing chemicals: pool shock, non-copper algaecide, and metal control if needed
- Winter plugs for returns and skimmer gizmos
- Non-toxic pool antifreeze (for plumbing lines only)
- O-ring lubricant and basic hand tools
- Safety or solid winter cover with straps, anchors, or water bags
Step-by-Step: How to Close a Fiberglass Pool for Winter
- Clean the Pool Thoroughly
Start by removing all leaves, twigs, and debris from the water. Vacuum the pool floor and brush down walls and steps to remove dirt and algae. The cleaner the pool is at closing, the clearer it will be when you reopen in spring.
- Test and Balance the Water
Balanced water protects your fiberglass surface and equipment. Adjust the chemistry to these ideal closing ranges:
- pH: 7.4–7.6
- Total Alkalinity: 80–120 ppm
- Calcium Hardness: 175–250 ppm
- Chlorine or Bromine: within normal range
If you’re unsure about your levels, bring a sample to Mock Pools & Ponds for accurate testing before adding closing chemicals.
- Add Pool Shock and Algaecide
Run the pump and circulate the water for at least 6–8 hours after adding a winter shock treatment and non-copper algaecide. This kills bacteria, prevents algae blooms, and ensures your pool stays clean during the off-season.
- Lower the Water Level (If Required)
If your system requires it, lower the water to about an inch below the bottom of the skimmer opening. Never drop the water too low in a fiberglass pool. The internal water pressure supports the shell and prevents structural damage.
- Blow Out and Plug the Lines
Use an air blower or shop vac to remove all water from return and suction lines. Once air is bubbling through the jets, plug each line to keep water out. Add a small amount of non-toxic pool antifreeze into each line for added freeze protection.
- Winterize the Skimmer
Blow out the skimmer line, pour a small amount of pool antifreeze into the line, and install a skimmer gizmo to absorb ice expansion. This protects the skimmer body and plumbing from cracking in freezing temperatures.
- Drain and Protect the Equipment
Turn off all power. Open the drain plugs on the pump, filter, heater, and chlorinator or salt cell. Remove pressure gauges and store them in a safe place. Lubricate O-rings and store drain plugs in the pump basket. Leave valves halfway open to prevent pressure damage from ice expansion.
- Remove Pool Accessories
Take out ladders, handrails, and other removable accessories. Rinse and dry them before storing indoors to prevent corrosion or staining.
- Install the Pool Cover
Install your safety or solid winter cover according to the manufacturer’s instructions. Ensure the cover is tight, secure, and properly anchored. This prevents wind lift, keeps debris out, and blocks sunlight to minimize algae growth over winter.
- Final Pool Closing Inspection
Check that all plumbing lines are sealed, equipment is drained, and the power supply is off. The water level should be correct and the cover tight. Label your breaker panel to prevent accidental use during the off-season.
After Closing Tips
- Periodically inspect your pool cover and remove snow or standing water.
- Avoid adding chemicals during winter.
- If water levels fluctuate significantly or you notice leaks or bubbling around fittings, schedule a service visit.
Common Mistakes to Avoid When Winterizing a Fiberglass Pool
- Lowering the water too far or draining completely.
- Forgetting to blow out plumbing lines before freezing weather.
- Leaving equipment sealed with water inside.
- Using copper-based algaecides that can stain fiberglass surfaces.
- Ignoring unbalanced water chemistry before closing.
Professional Pool Closing Services in Northeast Ohio
For homeowners who want a stress-free experience, Mock Pools & Ponds offers professional fiberglass pool closing services throughout Northeast Ohio. Our team can test and balance your water, winterize all plumbing and equipment, and secure your cover for total peace of mind.
Contact Mock Property Services at (330) 628-9100, Option #1 today to schedule your pool closing appointment and protect your investment for the season.