SLAM Protocol: Complete Guide for Pool Service Professionals

The SLAM protocol is the most effective systematic approach to treating algae, killing pathogens, and clearing green or cloudy water — and it's built on chemistry, not guesswork. Developed by the Trouble Free Pool community and validated by pool chemistry professionals, SLAM (Shock, Level, And Maintain) replaces the old "dump a bag of shock and hope" method with a structured, testable process. This guide covers everything you need to run it correctly for any customer.

What SLAM Is (and Isn't)

SLAM is not a one-time superchlorination. It is a sustained high-chlorine treatment where free chlorine is raised to a specific target — determined by the pool's CYA level — and held there continuously until three specific passing conditions are all met simultaneously.

The key distinction: most pool owners (and some techs) treat a green pool by adding shock, waiting a day, and calling it done. SLAM recognizes that killing algae requires maintaining bactericidal chlorine concentrations over time, not spiking once and letting levels drop.

Before You Start: Prerequisites

Running a SLAM on a pool that isn't balanced will waste time and chemicals. Before starting, confirm or adjust:

• pH: 7.2–7.5 — Lower end preferred during SLAM (7.2) because chlorine is more effective. High pH dramatically reduces HOCl concentration.
• CYA: 30–50 ppm — If CYA is above 90 ppm, SLAM FC targets become dangerously high. Partial drain required first.
• Alkalinity: 80–120 ppm — Adjust before starting to prevent pH from crashing during treatment
• Calcium hardness: 200–400 ppm — Not critical to SLAM efficacy, but prevents equipment damage during the process
• Filter: Clean and functional — A dirty filter loaded with dead algae will get clogged within hours of starting SLAM. Backwash or clean before beginning.

SLAM Chlorine Targets by CYA

This is the most important table in the protocol. FC targets must be maintained continuously — not just hit once. Use liquid chlorine (sodium hypochlorite, 10–12.5%) for dosing during SLAM, not trichlor, not cal-hypo in hard water. Every dose of trichlor adds more CYA and moves the goalposts.

Step-by-Step SLAM Procedure

Step 1: Balance pH First

Lower pH to 7.2 using muriatic acid before raising chlorine. This is critical — adding large amounts of sodium hypochlorite (which has a pH of ~13) to an already high-pH pool makes chlorine far less effective. Get pH right before touching FC.

Step 2: Raise FC to SLAM Target

Add liquid chlorine to hit your target level. Use a chlorine addition calculator based on pool volume, current FC, and target FC. Never add chlorine to the skimmer if you have a floater with trichlor in it — the concentrated mixing can create chlorine gas.

Step 3: Brush Everything

Brush all pool surfaces thoroughly — walls, floor, steps, behind ladders. Algae clings to surfaces in biofilm that chlorine can't penetrate without physical disruption. For black algae: use a stainless steel brush and be aggressive. Brush 2–3 times daily during SLAM.

Step 4: Run the Filter Continuously

No timers, no breaks. Pump runs 24/7 until the SLAM is complete. Dead algae must be filtered out, not left to decompose in the water. Clean the filter more aggressively than normal — check pressure every 8–12 hours. A filter loaded with dead algae will cause FC to drop rapidly as the organic material continues consuming chlorine.

Step 5: Test and Redose Every 2–4 Hours

During SLAM, test FC with a reliable FAS-DPD drop test (Taylor K-2006 or equivalent). Standard DPD colorimetric tests wash out above 10 ppm — they'll read zero even with 25 ppm FC. Use FAS-DPD exclusively during SLAM. Redose whenever FC drops below minimum threshold.

The Three Passing Conditions

SLAM is complete when ALL THREE of these conditions are met on the SAME day:

1. Water is clear: The pool bottom is clearly visible at the deep end. Not "pretty clear" — actually clear. Still slightly blue-green = not done.
2. Combined chlorine (CC) is below 0.5 ppm: Combined chlorine represents chloramines and organic chlorine demand. When CC is this low, the biological load has been eliminated.
3. Pass the OCLT: The overnight chlorine loss test. Measure FC at dusk, add any chlorine needed to reach target, then measure again at dawn (before sunlight hits the pool). FC loss must be 1 ppm or less over 8 hours. Loss greater than 1 ppm means active biological demand remains.

Common SLAM Mistakes

When to Drain Instead of SLAM

SLAM is not always the right answer. Recommend a partial or full drain when:

• CYA exceeds 90–100 ppm (SLAM FC targets exceed 40 ppm)
• Black algae with deep root penetration into plaster (chlorine cannot penetrate)
• TDS above 3,000 ppm in non-salt pools
• The customer has failed multiple SLAMs in one season — usually indicates an underlying flow or filtration problem
• Algae has been growing for months and the filter cannot handle the bioload