How to Fix a Green Pool: Step-by-Step SLAM Method Guide

Tools & Supplies Needed

Find on Amazon: Taylor K-2006C Pool Test Kit , Liquid Pool Chlorine , Muriatic Acid , Stainless Steel Pool Brush

Quick Answer

A green pool indicates algae growth that requires immediate chemical treatment. The most effective solution is the SLAM method (Shock Level And Maintain), which involves raising free chlorine to shock level based on your stabilizer (CYA) level and maintaining it continuously until the pool clears completely.

Step-by-Step SLAM Method to Clear Green Pool

1. Test Your Water Chemistry
   Use a reliable test kit like the Taylor K-2006C to measure:
   • Free Chlorine (FC)
   • Combined Chlorine (CC)
   • pH level
   • Total Alkalinity (TA)
   • Cyanuric Acid/Stabilizer (CYA)
   Record all readings as you'll need to retest frequently.
2. Balance pH First
   Lower pH to 7.2-7.4 using muriatic acid if above 7.6. High pH reduces chlorine effectiveness. Add 1 quart of muriatic acid per 10,000 gallons to lower pH by approximately 0.2 points. Wait 2 hours and retest before proceeding.
3. Calculate Your Shock Level
   Determine shock level based on CYA using the FC/CYA chart:
   • CYA 30: FC shock level 12 ppm
   • CYA 40: FC shock level 16 ppm
   • CYA 50: FC shock level 20 ppm
   • CYA 60: FC shock level 24 ppm
   • CYA 70: FC shock level 28 ppm
   • CYA 80: FC shock level 32 ppm
4. Add Liquid Chlorine to Reach Shock Level
   Use only liquid chlorine (sodium hypochlorite), not granular shock. Add approximately 1 gallon of 12.5% liquid chlorine per 10,000 gallons to raise FC by 10 ppm. Calculate total needed: if current FC is 2 ppm and shock level is 20 ppm, you need 18 ppm increase = 1.8 gallons per 10,000 gallons.
5. Start Continuous Filtration
   Run your pool pump and filter 24/7 throughout the SLAM process. Clean or backwash filter when pressure rises 10 psi above clean starting pressure. You may need to clean multiple times daily during heavy algae die-off.
6. Brush Pool Surfaces Thoroughly
   Brush walls, steps, corners, and behind ladders every few hours to break up algae colonies and expose them to chlorine. Use a stainless steel brush for plaster pools, nylon for vinyl/fiberglass.
7. Maintain Shock Level 24/7
   Test FC every 2-4 hours during daylight and add chlorine as needed to maintain shock level. Algae and sunlight will consume chlorine rapidly initially. As algae dies, chlorine demand will decrease.
8. Monitor Water Clarity Progress
   Typical progression: dark green → light green → cloudy blue → clear blue. This process usually takes 3-7 days depending on severity and pool maintenance.
9. Perform Overnight Chlorine Loss Test (OCLT)
   Once water appears clear blue, test FC in evening after sunset, then again 8-12 hours later before sunrise (with pump running). If FC drops more than 1 ppm overnight, continue SLAM process.
10. Final Steps When OCLT Passes
    When overnight FC loss is 1 ppm or less and water is crystal clear:
    • Stop adding chlorine
    • Allow FC to naturally drop to normal operating level (3-5 ppm for most CYA levels)
    • Resume normal pool maintenance schedule
    • Clean filter one final time

Important Safety Warnings

Never mix different types of chlorine or add chemicals simultaneously. Always add chemicals to water, not water to chemicals. Wear safety equipment when handling pool chemicals, and ensure adequate ventilation. Keep children and pets away from the pool during treatment.

Troubleshooting Common Issues

Pool Won't Clear After 7 Days

If your pool remains green after a week of proper SLAM:

• Verify you're maintaining true shock level using accurate test kit
• Check filter operation - may need professional cleaning or replacement
• Consider phosphate removal if levels exceed 500 ppb
• Test for metals (iron/copper) that may require metal sequestrant

Chlorine Demand Extremely High

If you're adding excessive chlorine with little FC increase:

• Verify CYA level isn't above 100 ppm (requires partial water replacement)
• Check for organic contamination requiring additional oxidation
• Ensure pH stays below 7.6 for maximum chlorine effectiveness

Prevention Tips

Prevent future green pool episodes by maintaining proper FC levels daily (based on your CYA level), running adequate filtration hours (typically 8-12 hours daily), and regular brushing and cleaning. Weekly water testing and prompt chemical adjustments prevent small problems from becoming major algae blooms.

The SLAM method typically costs $50-100 in chemicals but is far more effective than store-bought "algae treatments" that often fail to address the root cause. Most pool owners see significant improvement within 24-48 hours when following this protocol correctly.