Do I Need Pool Closing Chemicals? Complete Winter Guide

Tools & Supplies Needed

Find on Amazon: Taylor K-2006 Pool Test Kit , Winter Pool Algaecide , Pool Antifreeze , Pool Winterizing Kit

Quick Answer

Yes, you absolutely need pool closing chemicals to properly winterize your pool. These specialized chemicals prevent algae growth, protect your equipment from freeze damage, and ensure your pool opens clean and clear next season. The essential closing chemicals include winter algaecide, pool antifreeze, and maintaining proper sanitizer levels.

Step-by-Step Pool Closing Chemical Process

1. Balance Your Water Chemistry First
   Before adding any closing chemicals, test and adjust your water chemistry. Use a reliable test kit like the Taylor K-2006 to measure:
   • pH: Adjust to 7.2-7.6 using muriatic acid to lower or sodium carbonate to raise
   • Total Alkalinity: Target 80-120 ppm for most pools
   • Calcium Hardness: Aim for 150-300 ppm
   • Free Chlorine: Should be 1-3 ppm before adding closing chemicals
   Balanced water prevents staining, scaling, and corrosion during the closed season.
2. Shock the Pool 24-48 Hours Before Closing
   Add liquid chlorine or calcium hypochlorite shock to achieve 10-12 ppm free chlorine. This eliminates any bacteria or organic contaminants that could cause problems during winter. Use 1 gallon of 12.5% liquid chlorine per 10,000 gallons to raise chlorine by approximately 13 ppm. Allow the chlorine level to drop to 1-3 ppm before proceeding to the next step.
3. Add Winter Algaecide
   Apply a high-quality winter algaecide like BioGuard Arctic Blue or Leslie's Algae Away 60. These copper-based algaecides provide long-lasting protection against algae growth. Follow the manufacturer's dosage instructions, typically 1 quart per 15,000-20,000 gallons. Add the algaecide with the pump running and circulate for at least 2 hours to ensure even distribution.
4. Apply Pool Antifreeze to Plumbing Lines
   Pool antifreeze (propylene glycol) protects your plumbing from freeze damage. You'll need approximately 1 gallon of antifreeze per 10 feet of 1.5-inch pipe. Pour antifreeze into skimmer lines, return lines, and any other plumbing that cannot be completely drained. Never use automotive antifreeze, which is toxic and will damage your pool equipment.
5. Add Enzyme Products (Optional but Recommended)
   Enzyme-based products like Natural Chemistry Pool Perfect break down organic contaminants that accumulate during winter. Add according to package directions, typically 1 liter per 20,000 gallons. This step helps prevent waterline scum and reduces spring cleanup.
6. Consider a Winter Chemical Kit
   Many manufacturers offer complete winter closing kits that include algaecide, oxidizer, and metal sequestrant. These kits are sized for different pool volumes and take the guesswork out of chemical selection. Popular options include the In The Swim Winterizing Kit or the Pool Mate Winter Chemical Kit.

Regional Considerations for Closing Chemicals

Cold Climate Pools (Hard Freeze Areas)

In regions where temperatures consistently drop below 32°F, you'll need more aggressive winterization:

• Use maximum dosage of winter algaecide
• Ensure complete plumbing protection with antifreeze
• Consider adding a metal sequestrant if you have hard water
• Lower water level below skimmer and blow out all lines

Mild Climate Pools (Occasional Freeze)

In warmer regions with occasional freezing, you can use lighter chemical treatments:

• Standard algaecide dosage may be sufficient
• Focus antifreeze on exposed plumbing only
• Maintain higher water levels if no freeze risk
• Consider keeping equipment running during cold snaps

Critical Safety and Application Tips

Never mix pool chemicals together. Add each chemical separately with the pump running, allowing 2-4 hours between different chemical additions. Always add chemicals to water, never water to chemicals, and wear appropriate safety equipment including goggles and gloves.

Test your water chemistry again 24-48 hours after adding closing chemicals to ensure everything is properly balanced. Make final adjustments before completely shutting down your circulation system.

What Happens If You Skip Closing Chemicals

Pools closed without proper chemicals often experience:

• Severe algae blooms that require extensive SLAM treatment in spring
• Metal staining from unbalanced water chemistry
• Scale buildup on pool surfaces and equipment
• Freeze damage to inadequately protected plumbing
• Significantly higher opening costs and chemical requirements

The relatively small investment in closing chemicals saves hundreds of dollars in spring cleanup and potential equipment repairs. Proper winterization with the right chemicals ensures your pool opens clear, clean, and ready for another swimming season.