To clean a green pool, use the SLAM method: test and balance water chemistry, shock with liquid chlorine to reach shock level based on CYA, maintain that level until clear, then brush and vacuum debris.
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Cleaning a green pool requires the SLAM method (Shock Level And Maintain). First, test your water chemistry and balance pH to 7.2-7.6. Then add liquid chlorine to reach shock level based on your CYA (stabilizer) level, maintain that chlorine level until the pool clears, brush daily, and vacuum out dead algae debris.
Green pool water indicates algae growth, which occurs when chlorine levels drop too low to sanitize effectively. Common causes include equipment failure, inadequate chlorination, poor circulation, or chemical imbalances. The green color comes from chlorophyll in algae cells, and the intensity indicates the severity of the problem.
Before adding any chemicals, test your water using a reliable test kit like the Taylor K-2006C. You need accurate readings for:
If pH is above 7.6, lower it using muriatic acid before proceeding. High pH reduces chlorine effectiveness significantly.
Your shock level depends entirely on your CYA level. Use this FC/CYA relationship:
Warning: If your CYA exceeds 80 ppm, you'll need to partially drain and refill your pool before proceeding, as shock levels become impractically high.
Use liquid chlorine (sodium hypochlorite), not granular "pool shock" from stores. Calculate dosing: 1 gallon of 10% liquid chlorine raises FC by approximately 1.5 ppm in 10,000 gallons of water. Add chlorine in the evening to minimize sun degradation, pouring around the pool perimeter with circulation running.
Test FC levels twice daily (morning and evening) and add chlorine as needed to maintain shock level. Initially, chlorine will drop rapidly as it kills algae. This process typically takes 3-7 days depending on algae severity. The pool will gradually change from green to cloudy white/blue, then clear.
Brush your pool walls, steps, and floor thoroughly twice daily using a steel brush for concrete pools or nylon brush for vinyl/fiberglass. Brushing dislodges algae from surfaces, allowing chlorine to kill it more effectively. Run your filtration system 24/7 during the SLAM process.
Clean your filter every 2-3 days during SLAM. For sand filters, backwash when pressure rises 8-10 psi above clean pressure. For cartridge filters, rinse with a hose or replace if severely clogged. DE filters should be backwashed and recharged with fresh DE.
Your SLAM is complete when you achieve all three criteria:
Once complete, vacuum the pool thoroughly to remove dead algae debris. You may need to vacuum to waste if debris is heavy, then refill and rebalance as needed.
Never use algaecide during SLAM - it interferes with chlorine and prolongs the process. Avoid using trichlor tablets or granular shock, as these contain CYA and will raise your stabilizer levels. Don't rush the process by adding extra chlorine beyond shock level - this wastes money without improving results.
Maintain proper pH throughout SLAM. If pH drifts above 7.6, add muriatic acid immediately. High pH can stall the entire process.
Maintain proper FC levels based on your CYA (typically 3-5 ppm for 30-50 CYA). Test water 2-3 times weekly during swimming season. Ensure adequate circulation - run pumps long enough to turn over your entire pool volume daily. Keep pH between 7.4-7.6 and TA properly balanced.
Regular brushing prevents algae attachment, especially in areas with poor circulation. Address equipment problems immediately, and never let chlorine levels drop to zero.
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