SLAM (Shock Level And Maintain)
Deep-clean your pool when algae blooms or FC demand spikes beyond normal correction.
Log your actual chemistry to get a personalized SLAM target and track your progress throughout the process.
SLAM Playbook
Shock Level And Maintain - Eliminate algae and restore crystal clear water
What is SLAM?
SLAM stands for Shock Level And Maintain. It's a scientifically-proven method to eliminate algae and organic contamination from your pool using only chlorine - no expensive chemicals or algaecides needed.
Think of SLAM as a "chlorine bath" for your pool. You raise Free Chlorine (FC) to a very high level based on your Cyanuric Acid (CYA), then maintain that level continuously until all algae is completely dead and oxidized. The high chlorine level overwhelms the algae's ability to survive.
The Science:
- • Normal FC (2-4 ppm): Prevents algae from starting
- • SLAM FC (12 ppm): Kills existing algae actively growing
- • Why 40% of CYA? CYA "binds" to chlorine, reducing effectiveness. Higher CYA = higher FC needed to kill algae
- • Why maintain continuously? Algae recovers quickly if FC drops. You must maintain pressure until it's 100% dead.
Do You Need to SLAM?
SLAM when you have visible algae growth or Combined Chlorine (CC) that won't clear. Don't SLAM unless necessary - it's time-intensive and prevents swimming.
✓ SLAM is the solution:
- • Green, yellow, or black water
- • Visible algae on walls/floor
- • Cloudy water that won't clear
- • CC consistently > 0.5 ppm
- • Mustard or black algae
- • Post-neglect recovery
✗ Don't SLAM for:
- • Slightly cloudy water (check filter)
- • Minor pH imbalance
- • Routine maintenance
- • "Just to be safe"
- • Stains (metal or mineral issues)
- • Sand/dirt in pool (physical debris)
Light algae: 3-7 days
Heavy green: 7-14 days
Black algae: 14-21 days
20k gal pool, moderate algae
10-30 gal liquid chlorine
@$3-5/gallon
Taylor K-2006 or equivalent
Test strips will NOT work
FAS-DPD method required
Your SLAM Target
Maintain FC at 12 ppm (40% of CYA 30 ppm) throughout the process
- • NO swimming during SLAM (FC levels are irritating/unsafe)
- • Do NOT add algaecide, clarifier, or phosphate remover
- • Do NOT shock with cal-hypo or dichlor during SLAM
- • Only adjust pH if it exceeds 8.0 (high pH reduces FC effectiveness)
- • Process takes 3-14 days depending on algae severity
- MYTH: "Algaecide speeds up SLAM"
REALITY: Algaecide adds copper/quaternary compounds that interfere with FC. Chlorine alone kills algae. - MYTH: "Drain and refill is faster than SLAM"
REALITY: Draining doesn't kill algae on surfaces - it returns immediately. SLAM eliminates the root cause. - MYTH: "You can SLAM with tablets or cal-hypo"
REALITY: Tablets add CYA (raising SLAM target), cal-hypo raises pH/CH. Only liquid chlorine maintains control. - MYTH: "Cloudy white water means SLAM failed"
REALITY: Dead algae turns white before filtering out. This is progress - keep filtering and brushing.
Prepare & Test
Verify your chemistry baseline and gather supplies before starting.
Raise FC to SLAM Level
Add liquid chlorine to raise FC to 12 ppm (40% of your CYA).
Maintain SLAM Level
Keep FC at SLAM level continuously - any drop lets algae recover. This is the most critical phase.
Monitor for Completion
Track three strict criteria - ALL must pass before stopping SLAM. No shortcuts!
Exit SLAM & Resume Normal
Verify completion criteria hold, then transition back to maintenance mode.
Frequently Asked Questions
Why does my FC keep dropping so fast?
Algae and organic matter consume chlorine rapidly through oxidation. Heavy algae blooms can drop FC 10+ ppm overnight, especially in the first 2-3 days. This is completely normal early in SLAM - it means the chlorine is working! Keep adding chlorine to maintain SLAM level until consumption slows. Think of it like bailing water from a leaky boat - once you patch the leaks (kill the algae), the water level stays stable.
Can I speed up SLAM by raising FC even higher?
No. The 40% CYA ratio is scientifically optimal - going higher wastes money without faster results and risks bleaching pool surfaces. The limiting factor is contact time and surface area, not chlorine concentration. Focus on consistent SLAM level maintenance and thorough brushing (2x daily minimum) instead. Brushing dislodges algae so chlorine can reach it - this speeds SLAM more than extra chlorine.
My water turned cloudy white during SLAM - did I do something wrong?
No - this is actually GOOD news! Dead algae turns white/gray before being filtered out (like meat turning white when cooked). This cloudiness is suspended dead algae particles. Continue SLAM, run pump 24/7, and clean/backwash filter as needed. Clarity returns in 2-4 days as the filter removes debris. Do NOT drain, add clarifier, or add flocculant - these interfere with the process. Be patient and let your filter do its job.
How much will SLAM cost in total?
For a 20,000 gallon pool with moderate algae: expect 10-20 gallons of liquid chlorine (~$40-80 total) over 5-7 days. Severe green swamp cases may require 30-40 gallons (~$120-160). Black algae can use 50+ gallons over 14-21 days. Cost varies by chlorine price ($3-5/gal), pool volume, and algae severity. Still WAY cheaper than draining/refilling or hiring a pool service to do the same thing!
Should I backwash/clean my filter during SLAM?
Yes, but only when pressure rises 25% above clean baseline (e.g., 10 psi → 12.5 psi). Over-cleaning removes beneficial filter "cake" (a layer of debris that actually improves filtration by catching smaller particles). For cartridge filters, clean when flow visibly decreases or pressure rises. For sand/DE filters, backwash when pressure increases. You'll likely clean/backwash 2-4 times during a typical SLAM.
Can I swim during SLAM?
NO. SLAM FC levels (typically 12-32 ppm) can irritate skin, eyes, and respiratory system. It's also unsafe - you could bleach swimsuits and the high chlorine can be harsh. Wait until SLAM completes and FC drops back to normal range (2-4 ppm) via sunlight degradation. This usually takes 1-3 days after stopping chlorine additions. Safety first!
What if I have a salt water chlorine generator (SWCG)?
Turn OFF your SWCG during SLAM. SWCGs can't produce chlorine fast enough to maintain SLAM levels - you'll burn out the cell trying. Use liquid chlorine exclusively. Once SLAM completes, turn the SWCG back on and resume normal operation. The high FC during SLAM won't harm the cell, but running it during SLAM will cause unnecessary wear.
Why can't I use tablets or cal-hypo for SLAM?
Tablets (trichlor): Add CYA with every dose, constantly raising your SLAM target. You'll be chasing an ever-increasing FC requirement - a losing battle. Cal-hypo: Raises pH and calcium hardness dramatically, causing water balance nightmares and potential scaling. Liquid chlorine(sodium hypochlorite) adds only chlorine with minimal pH impact - it's the ONLY chemical that works for SLAM.
I passed OCLT once, can I stop SLAM?
NO! You need to pass OCLT (≤1.0 ppm loss) for 2-3 consecutive nights, AND have crystal clear water, AND have CC ≤ 0.5 ppm. All three criteria must hold for multiple days. Stopping early is the #1 reason SLAMs fail - microscopic algae remains and blooms again in 2-3 weeks, forcing you to start over. Patience now = permanent success.
Can I do a partial drain instead of SLAM?
No. Draining doesn't kill algae on pool surfaces - it just removes water. The algae clings to walls, floor, and equipment, then re-blooms immediately when you refill. SLAM is the ONLY way to truly eliminate algae by oxidizing it completely. The only time to drain is if CYA > 80 ppm (to lower CYA before starting SLAM) or for physical repairs. Otherwise, draining is a waste of water and money.
What happens if I give up mid-SLAM?
Algae recovers and you're back to square one - all chlorine and time wasted. Partially-killed algae actually adapts and becomes harder to eliminate next time. It's like taking half a course of antibiotics - you don't cure the infection, you just create resistant bacteria. Commit fully or don't start. If you absolutely must quit, at least maintain normal FC levels (7.5% of CYA) to prevent re-bloom while you regroup and gather resources to restart.
Pro Tips for SLAM Success
- ✓Keep a SLAM log: Record FC readings, chlorine added, and observations daily. Helps predict dosing needs and track progress.
- ✓Brush before testing FC: Dislodges algae into water where chlorine can kill it. Brushing after adding chlorine helps too.
- ✓Test at same times daily: Morning and evening FC tests show consumption patterns and help predict overnight needs.
- ✓Buy chlorine in bulk: Purchase 10-15 gallons at start. Running out mid-SLAM wastes previous progress if FC drops too low.
- ✓Don't adjust TA during SLAM: Wait until completion. Only adjust pH if it exceeds 8.0 (reduces chlorine effectiveness).
- ✓Run pump continuously: Use a timer override or breaker if needed. Stagnant water = algae safe zones. Circulation is critical.
- ✓Clean skimmer/pump baskets daily: Debris blocks flow and reduces filtration efficiency. Empty baskets = better circulation.
- ✓Use Poolometer's OCLT tracker: Log your evening/morning FC readings to track SLAM progress scientifically.
Checklist
- 1Collect full chemistry and confirm CYA level.
- 2Lower pH to 7.2 before starting.
- 3Raise FC to SLAM target (40% of CYA) and maintain with frequent testing.
- 4Brush and filter continuously until pass criteria.
- 5Verify crystal clarity, <1 ppm OCLT, and CC ≤ 0.5 to exit.
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