Swimming Pool SLAM Calculator

Pool SLAM Calculator | Shock Level And Maintain
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Pool SLAM Calculator

Calculate precise chlorine dosing to Shock Level And Maintain.
TFP Method Algae Kill Liquid Chlorine
Your required SLAM level is completely dictated by your CYA.
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Pool size
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Levels
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Chlorine
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What is the SLAM Method?

SLAM stands for Shock Level And Maintain. It is widely considered the most effective, foolproof method for eradicating green, cloudy, or algae-infested pool water.

Traditional “pool store” advice tells you to throw in a few bags of shock and hope for the best. The problem with this is that chlorine gets consumed rapidly by the algae and the sun. Within hours, your chlorine levels drop to zero, and the surviving algae simply grows right back. You end up on an endless, expensive rollercoaster.

The SLAM method solves this by introducing the “Maintain” step. You elevate your Free Chlorine (FC) to a specific “Shock Level,” and you aggressively re-test and re-dose the pool multiple times a day to maintain that exact high level. The algae is never given a chance to recover, resulting in crystal clear water.

Required Equipment: You cannot perform a SLAM with standard test strips or a basic OTO drop kit (the one that turns yellow). Those tests max out at 5 ppm. To measure SLAM levels (which often exceed 15-20 ppm), you must have a FAS-DPD drop test kit like the Taylor K-2006.

The CYA / Chlorine Relationship

The single most important rule of pool chemistry is that your required Free Chlorine level is directly dictated by your Cyanuric Acid (CYA) level. CYA (also known as stabilizer or conditioner) protects chlorine from the sun, but it also buffers its strength.

If you have 0 CYA, an FC of 3 ppm is incredibly strong. If you have 100 CYA, an FC of 3 ppm is so weak that algae will grow effortlessly.

Because of this relationship, your target SLAM FC level scales based on your CYA. The general formula is roughly 40% of your CYA level. For example, if your CYA is 40, your SLAM target is 16 ppm.

Why Liquid Chlorine is Best for SLAM

We heavily recommend using Liquid Chlorine (Sodium Hypochlorite) or household bleach for a SLAM. Here’s why:

  • Powdered Shock (Dichlor / Trichlor): Contains CYA. Every time you add it, your CYA goes up. This raises your required SLAM target, moving the goalposts and making it infinitely harder to clear the pool.
  • Powdered Shock (Cal-Hypo): Contains Calcium. Adding massive amounts during a SLAM will skyrocket your Calcium Hardness, which can cause severe scaling on your pool walls and equipment.
  • Liquid Chlorine: Contains only chlorine, water, and a tiny bit of salt. It leaves nothing harmful behind. It goes in, kills the algae, and breaks down under the sun.

Step-by-Step SLAM Guide

Before you begin, make sure you know your pool’s exact volume in gallons. If you’re unsure, determine your pool volume using our free Pool Volume Calculator.

  1. Test and Adjust pH: Accurately test your pH and lower it to between 7.2 and 7.4. You can use our pH Calculator to determine exactly how much acid to add. (Extremely high chlorine levels will cause pH tests to read falsely high, so you must adjust this before you begin).
  2. Check Alkalinity: For a stable pH, your Total Alkalinity should be between 60 and 90 ppm. If it’s off, get precise dosing with our Pool Alkalinity Calculator.
  3. Find your Target: Test your CYA level. Input it into the calculator above to find your target SLAM FC level.
  4. Initial Dose: Test your current FC. Use the calculator to determine how much liquid chlorine you need to reach your target, and pour it into the pool with the pump running.
  5. Brush: Brush the entire pool (walls and floor). Algae builds a protective slime coat; brushing tears it off.
  6. Maintain: Come back 2 to 4 hours later. Test your FC again with your FAS-DPD kit. It will likely have dropped significantly. Use the calculator to figure out the new deficit, add that amount of chlorine, and brush again.
  7. Repeat: Continue testing and adding chlorine 2 to 4 times a day. Do not let the FC drop!

How Do I Know When I’m Done?

You are officially finished with the SLAM when your pool meets all three of these criteria simultaneously:

  1. Crystal Clear Water: The water is completely transparent. You should be able to clearly see the screws on the main drain in the deep end. No cloudiness.
  2. No Combined Chlorine (CC): Your CC level is 0.5 ppm or lower, meaning the chlorine is no longer actively fighting a large organic load.
  3. Pass the Overnight Chlorine Drop Test (OCDT): Test your FC after the sun goes down. Test it again the next morning before the sun hits the pool. If your FC dropped by 1.0 ppm or less, it means nothing grew overnight. You are done!

Once your pool passes all three tests, you can stop SLAMing and rely on our Pool Chlorine Calculator for accurate daily dosing.

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