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Specialty & Niche · L3

SLAM (Shock Level And Maintain) Protocol Calculator

The CYA-based shock level to kill algae and hold it — plus duration and the OCLT pass test.

Measure the inputsSLAM means holding a high, CYA-based chlorine level — not one big dose.
Read the full resultTest and re-dose several times a day to keep FC at the SLAM target.
Check the boundaryBrush the pool daily; black and mustard algae especially need scrubbing.

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Live calculation

SLAM inputs

✓ Checked May 2026

Enter volume, current FC, CYA, and condition.

Change a value. See the result.

Required fields are marked *. Engine validation and warnings remain active.

Enter the known values. Let the engine handle the calculation.

✓ Formula checked↻ Live result○ No account needed

Planning estimate only. Confirm product labels, equipment specifications, qualified-professional advice and local requirements before acting.

The result, explained

Use the SLAM (Shock Level And Maintain) Protocol Calculator result with context.

The CYA-based shock level to kill algae and hold it — plus duration and the OCLT pass test.

01

The purpose

What does this calculator estimate?

The CYA-based shock level to kill algae and hold it — plus duration and the OCLT pass test.

02

The tool

What information does it use?

  • Pool volume: enter a measured or verified value
  • Current free chlorine: ppm
  • Cyanuric acid: Sets the SLAM target FC.
  • Pool condition: Cloudy, green, black, or mustard algae.
  • Chlorine product: Liquid 12.5% or cal-hypo 65%.
  • Daily FC loss: ppm/day consumed during the SLAM.
03

The method

How to use this calculator

  1. Pool volumeEnter the value you can verify.
  2. Current free chlorineppm
  3. Cyanuric acidSets the SLAM target FC.
  4. Pool conditionCloudy, green, black, or mustard algae.
  5. Chlorine productLiquid 12.5% or cal-hypo 65%.
  6. Daily FC lossppm/day consumed during the SLAM.
04

The relationship

The formula in plain English

SLAM target FC = CYA × 0.4 (minimum 12 ppm)

Hold the target until OCLT < 1 ppm overnight loss, CC < 0.5 ppm, and water is clear.
05

Worked through

A worked example: 15,000-gal green pool, CYA 40, FC 1.0

  1. SLAM target = 40 × 0.4 = 16 ppm
  2. Initial dose: raise FC 1 → 16 ppm
  3. Hold 16 ppm, re-dosing; green algae ≈ 3–7 days
SLAM target free chlorine by cyanuric acid level.
CYA levelSLAM target FC (CYA × 0.4)Normal min FC
20 ppm12 ppm (min floor)1.5 ppm
30 ppm12 ppm2.3 ppm
40 ppm16 ppm3.0 ppm
50 ppm20 ppm3.8 ppm
60 ppm24 ppm4.5 ppm
06

Why it matters

How the result supports the next decision

SLAM means holding a high, CYA-based chlorine level — not one big dose.

Test and re-dose several times a day to keep FC at the SLAM target.

07

Good inputs

Improve the estimate before relying on it

  • SLAM means holding a high, CYA-based chlorine level — not one big dose.
  • Test and re-dose several times a day to keep FC at the SLAM target.
  • Brush the pool daily; black and mustard algae especially need scrubbing.
  • The SLAM is done only when OCLT, combined chlorine, and clarity all pass.
  • Keep swimmers out until FC falls back into the normal range.
08

The boundary

How to interpret the result

Measurements, equipment specifications, site conditions and local requirements can change the practical result.

The engine reports invalid inputs and safety warnings beside the result. Resolve those messages before using the estimate.

09

Before acting

What should override this estimate?

  • Measured site conditions and current test results
  • Product labels and manufacturer specifications
  • Qualified-professional advice and applicable local codes
10

Common questions

Frequently asked questions

What is the SLAM method?

SLAM stands for Shock Level And Maintain. You raise free chlorine to a target based on your cyanuric acid level — about 40 percent of CYA — and hold it there with repeated dosing until the algae is dead and the water passes a set of tests. It's a sustained process, not a single shock.

How do I calculate the SLAM chlorine level?

Multiply your cyanuric acid by 0.4 to get the target free chlorine. So at CYA 40, the SLAM level is 16 ppm; at CYA 30, it's 12 ppm. If CYA is zero or very low, use a minimum of 12 ppm. You then maintain that level continuously, re-dosing as the chlorine is consumed.

How long does a SLAM take?

It depends on the algae: cloudy water clears in 1 to 3 days, green algae in 3 to 7 days, mustard algae in 3 to 5 days, and stubborn black algae in 7 to 14 days with daily brushing. The SLAM continues until the pass tests are met, however long that takes — you don't stop early.

How do I know when the SLAM is finished?

Three criteria must all pass: the overnight chlorine loss test (OCLT) shows less than 1 ppm of free chlorine lost overnight, combined chlorine is below 0.5 ppm, and the water is clear. Until all three pass, algae is still present and consuming chlorine, so you keep maintaining the SLAM level.

What is the OCLT?

The Overnight Chlorine Loss Test measures how much free chlorine the pool consumes overnight, when there's no sunlight to burn it off. You record FC at dusk and again at dawn. A loss under 1 ppm means no significant organic load remains feeding chlorine demand — one of the three signals the SLAM is complete.

How do you calculate SLAM level?

SLAM free chlorine target = CYA × 0.4, with a minimum of 12 ppm.

How long does a SLAM take to clear algae?

Cloudy 1–3 days, green 3–7, mustard 3–5, black 7–14 days with brushing.

When is a SLAM complete?

When OCLT loss is under 1 ppm, combined chlorine is below 0.5 ppm, and the water is clear.

Primary sources

Use the result with current guidance.

These official references support safe planning context. Product labels, local requirements and qualified-professional advice take priority over a general calculator estimate.