Can You Close a Green Pool? Complete Winter Closing Guide

Tools & Supplies Needed

Find on Amazon: Taylor K-2006 Pool Test Kit , Liquid Chlorine Pool Shock , Copper-Based Pool Algaecide , Pool Winterizing Chemical Kit

Quick Answer

Yes, you can technically close a green pool, but it's strongly discouraged unless absolutely necessary. Closing a pool with active algae will likely result in a severely contaminated, potentially black pool come spring that will require extensive treatment and possibly equipment replacement. However, if you must close a green pool due to time or budget constraints, specific steps can minimize the damage.

Why Closing a Green Pool Is Problematic

Algae doesn't simply go dormant during winter—it continues to grow and multiply even in cold water, albeit more slowly. When you close a green pool without proper treatment, several problems compound over the winter months:

• Algae blooms will intensify, often progressing from green to black algae
• Dead organic matter will accumulate on pool surfaces and in equipment
• pH levels will drop significantly as algae decomposes
• Metal staining may occur from decomposing algae and unbalanced water
• Equipment damage from prolonged exposure to contaminated water
• Potential liner or surface damage from aggressive spring treatments needed

Option 1: Treat Before Closing (Recommended)

The best approach is performing a SLAM (Shock Level And Maintain) treatment before winterizing. This process typically takes 3-7 days but ensures a clean opening:

1. Test water chemistry using a Taylor K-2006 test kit, measuring FC, pH, CYA, and TA
2. Balance pH first to 7.2-7.4 using muriatic acid if needed
3. Determine shock level based on your CYA reading using the FC/CYA chart (typically 10-12 ppm FC for 30-50 ppm CYA)
4. Add liquid chlorine to reach shock level—expect to use 3-5 gallons per 10,000 gallons of water initially
5. Run pump continuously during SLAM treatment, backwashing or cleaning filter every 12-24 hours
6. Maintain shock level by testing and adding chlorine every 12 hours until overnight FC loss is 1 ppm or less
7. Brush pool surfaces twice daily to dislodge algae, paying attention to corners and steps
8. Vacuum waste rather than filtering dead algae back into the pool
9. Test for completion when water is crystal clear and passes overnight chlorine loss test
10. Balance final chemistry before beginning normal winterizing procedures

Option 2: Emergency Green Pool Closing

If you absolutely must close a green pool without treatment, follow these damage-minimization steps:

Pre-Closing Preparation

1. Remove large debris manually—don't run automated cleaners in green water
2. Add extra algaecide—use 2-3 times the normal closing dose of copper-based algaecide
3. Shock heavily with 3-4 lbs of calcium hypochlorite per 10,000 gallons
4. Add winterizing chemicals at 150% of recommended dosage
5. Lower water level more than usual (6-8 inches below skimmer) to account for potential staining

Equipment Protection

1. Drain all equipment thoroughly—contaminated water is more likely to damage pipes and fittings
2. Remove pump basket and skimmer baskets for thorough cleaning
3. Add extra pool antifreeze to all lines—use 25% more than normal
4. Consider removing expensive equipment like salt cells, heater elements, or automation systems

Cover Installation

• Use a tight-fitting safety cover rather than a winter cover to minimize debris and light penetration
• Ensure complete coverage to prevent photosynthesis from worsening algae growth
• Consider using cover clips every 18 inches instead of every 24 inches for extra security

Spring Opening Expectations

If you closed a green pool, prepare for intensive spring treatment:

• Budget for 5-10 gallons of liquid chlorine initially
• Plan for multiple filter cleanings or replacements
• Expect 1-2 weeks of SLAM treatment minimum
• Consider professional equipment cleaning or replacement
• Budget for potential surface cleaning or acid washing

Cost Considerations

Treating before closing costs approximately $50-100 in chemicals and time investment. Closing green and dealing with consequences typically costs $200-500 in spring chemicals, equipment repairs, and potential professional services. The math strongly favors treating first.

Prevention for Next Season

To avoid this situation in future seasons:

• Begin closing preparations while water is still clear
• Maintain proper sanitizer levels through late season
• Address algae problems immediately when they appear
• Test CYA levels mid-season to ensure proper chlorine effectiveness
• Keep backup liquid chlorine on hand for emergency treatments

When Professional Help Is Needed

Contact a pool professional if: your CYA levels exceed 100 ppm, you're dealing with black algae spots, equipment appears damaged, or you're uncomfortable handling large quantities of chemicals. Some situations require partial drain and refill before any treatment is effective.