The SLAM method (Shock Level And Maintain) clears green pools by maintaining high chlorine levels continuously until water clears. Use liquid chlorine to reach shock level based on CYA, maintain 24/7 until overnight chlorine loss is 1ppm or less.
The SLAM method (Shock Level And Maintain) is the most effective way to clear a green pool caused by algae. This process involves raising your pool's free chlorine (FC) to shock level based on your cyanuric acid (CYA) level and maintaining that level continuously until the water clears and passes the overnight chlorine loss test.
Key Requirements:
SLAM stands for "Shock Level And Maintain" - a systematic approach to eliminate algae by overwhelming it with continuous high chlorine levels. Unlike traditional shocking methods where you add chlorine and wait, SLAM requires maintaining shock-level chlorine around the clock until the algae is completely dead.
Many pool owners ask if they need to shock weekly, but regular shocking often fails against established algae blooms. SLAM succeeds because:
Before starting SLAM, understand these critical relationships:
Free Chlorine to CYA Ratio: Your shock level depends entirely on your CYA level. Higher CYA requires proportionally higher FC to achieve the same sanitizing effect.
Shock Level Chart (FC based on CYA):
Step 1: Test Your Water Chemistry
Use a quality test kit (Taylor K-2006 or TF-100) to measure:
Never rely on test strips for SLAM - they're too inaccurate for the precision required.
Step 2: Balance pH First
Lower pH to 7.2-7.4 before starting. High pH reduces chlorine effectiveness significantly. If pH is above 7.6, adjust it down using muriatic acid.
Step 3: Check and Adjust Alkalinity
Ensure alkalinity is in proper range (80-120ppm for most pools) to prevent pH bounce during SLAM.
Step 4: Calculate Chlorine Needed
Determine how much liquid chlorine to add based on:
Use this formula: (Target FC - Current FC) × Pool Gallons ÷ 120,000 = Gallons of 12.5% liquid chlorine needed
Step 5: Add Liquid Chlorine
Add chlorine gradually around the pool perimeter with pump running. Never pour directly into skimmer.
Step 6: Begin Continuous Filtration
Run your filter system 24/7 throughout SLAM. Continuous filtration is safe and beneficial for removing dead algae and maintaining water circulation.
Step 7: Test and Maintain Every 2-4 Hours
During active SLAM, test FC every 2-4 hours and add chlorine to maintain shock level. Algae and organic matter will consume chlorine rapidly initially.
Step 8: Brush Pool Surfaces Twice Daily
Brush walls, steps, and all surfaces twice daily to dislodge algae and improve chlorine contact. Focus on areas with visible algae growth.
Step 9: Vacuum and Clean Filter
You can vacuum after adding chemicals, but wait 15-30 minutes for circulation. Clean your filter frequently as it captures dead algae.
Step 10: Monitor Water Clarity
Water should progressively clear from green to cloudy white to crystal clear. Cloudy water during SLAM is normal as dead algae is filtered out.
Step 11: Perform Overnight Chlorine Loss Test
When water appears clear:
SLAM is complete when overnight loss is 1ppm or less for two consecutive nights.
Backwash sand filters when pressure gauge reads 8-10 psi above clean starting pressure. During heavy SLAM, this might be daily initially.
Deep clean filter sand if backwashing doesn't restore proper flow. Consider replacing sand if it's over 5 years old.
Cartridge filters cannot be backwashed - they must be physically cleaned. Have spare cartridges available for rotation during SLAM.
Clean cartridges daily during active SLAM using a filter cleaner solution and high-pressure rinse.
DE filters require regular backwashing during SLAM, potentially every 24-48 hours initially. Recharge with fresh DE powder after each backwash.
Cause: Heavy algae load or high chlorine demand
Solution:
Cause: Filter issues or inadequate circulation
Solution:
Cause: Liquid chlorine has high pH (around 13)
Solution:
Possible Causes:
Solutions:
Most pools need 8-12 hours daily normally, but SLAM requires 24/7 operation. Ensure your pump can handle continuous operation.
Never run pool pumps on extension cords - the continuous high-amperage draw during SLAM makes this extremely dangerous.
You'll need a pool vacuum to remove settled algae debris during SLAM. Manual vacuums work well, but robotic cleaners can help with continuous cleaning.
Store liquid chlorine in a cool, dry place away from direct sunlight. Buy fresh chlorine frequently during SLAM as you'll use large quantities.
Wait 4-6 hours between adding different chemicals to prevent dangerous reactions.
Wear safety goggles and gloves when handling chemicals. Work upwind when adding chlorine to avoid inhaling fumes.
Day 1: Water may get cloudier as algae dies
Days 2-3: Green color fades to cloudy white
Days 4-7: Gradual clearing from bottom up
Final days: Crystal clear water with stable overnight chlorine loss
Expect to use 3-10 gallons of liquid chlorine total, depending on pool size and algae severity. This is far more cost-effective than repeated store-bought shock treatments.
Once SLAM is complete:
Consider professional help if:
You may need a new pump if yours fails during the continuous operation required for SLAM.
Consider filter replacement if cleaning doesn't restore proper flow during SLAM.
Saltwater pools still need proper chemistry for SLAM. Turn off the salt generator and use liquid chlorine exclusively during the process.
Saltwater pools need CYA just like traditional pools, so follow the same FC/CYA ratios.
Above ground pools follow the same SLAM process but may clear faster due to smaller volume and easier access for brushing.
If SLAM is needed before winter closing, complete the entire process before winterization. Never close a green pool.
Shock your pool before winter closing, but only after completing SLAM if algae was present.
No, never swim during SLAM. Chlorine levels are dangerously high (10-30+ ppm) and can cause chemical burns, respiratory issues, and equipment damage to swimsuits.
Expect $30-100 in liquid chlorine costs depending on pool size and algae severity. This is much cheaper than draining and refilling or hiring a service company.
Properly executed SLAM won't damage equipment. High chlorine levels are temporary and within equipment tolerance ranges.
No, use only liquid chlorine. Calcium hypochlorite (shock granules) adds calcium and can cause cloudiness. Dichlor/trichlor adds CYA, making SLAM less effective.
If CYA exceeds 80-100ppm, partially drain and refill before starting SLAM. High CYA makes the process ineffective and expensive.
Complete SLAM success requires: crystal clear water, overnight FC loss ≤1ppm for two consecutive nights, and no visible algae anywhere in the pool.
No shortcuts exist. The process takes as long as needed to kill all algae. Attempting to rush by under-dosing chlorine will fail and waste time and money.
For comprehensive pool care knowledge, explore these related guides:
The SLAM method is the gold standard for clearing green pools because it works reliably when executed properly. While intensive, it saves money compared to alternatives and ensures complete algae elimination. Success requires patience, proper chemistry knowledge, and consistent execution of the process until completion criteria are met.
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