How to SLAM Your Pool: Clear Green Water Fast

You walked outside and your pool is green. Maybe light green, maybe swamp-green. Either way, you need it fixed yesterday. The SLAM method - Shock Level and Maintain - is the most effective way to clear a green pool, and it's exactly what we use on every green pool recovery call. Here's exactly how it works, step by step.

What Is SLAM?

SLAM stands for Shock Level and Maintain. It's not just dumping a bunch of shock in your pool and hoping for the best. It's a methodical process of raising your chlorine to shock level (based on your CYA) and keeping it there until all the algae is dead and your water passes three tests:

1. Your water is clear (no cloudiness or visible algae)
2. You pass the Overnight Chlorine Loss Test (OCLT)
3. Your CC (combined chlorine) is 0.5 or below

Skipping any of these means your algae will come right back - usually within a week.

Why Most Pool Owners Fail at Clearing Green Pools

Here's what most people do: buy a couple bags of shock at the pool store, dump them in, and wake up the next morning to... still-green water. Then they buy more shock. Then they give up and call us.

The problem isn't the amount of shock - it's the CYA (cyanuric acid) level. If your stabilizer is high, normal shock levels won't kill anything. The FC/CYA relationship determines how much chlorine you actually need, and most pool store advice completely ignores this.

That's why we always start with a proper test kit - not strips, not the pool store printout. You need to know your exact FC, CC, pH, TA, CH, and CYA before you start a SLAM.

Step 1: Test Your Water

Before you add anything, test your water with a proper test kit (we recommend a FAS-DPD test kit like the Taylor K-2006). You need to know:

• pH - must be between 7.2 and 7.8 before you SLAM. Lower if above 7.8.
• CYA (stabilizer) - this determines your shock level. Higher CYA = higher shock level.
• FC (free chlorine) - where you're starting from.
• CC (combined chlorine) - should be near zero when the SLAM is complete.

Step 2: Calculate Your Shock Level

Your shock level depends on your CYA. Here's the basic chart:

If your CYA is above 70, you may need to drain some water first. In Texas, where CYA climbs fast from tabs and sunshine, this is common. We see pools with CYA over 100 all the time - and those pools will never clear until the stabilizer comes down.

Step 3: Add Chlorine and Maintain Shock Level

Use liquid chlorine (sodium hypochlorite, 10-12.5%) - not granular shock. Granular adds CYA or calcium, which you don't need more of during a SLAM.

• Add enough chlorine to reach your shock level based on the chart above
• Brush the entire pool - walls, floor, steps, ladders, behind the ladder, under the skimmer
• Run the pump 24/7 - no exceptions
• Test and add chlorine every 2-4 hours during the day to maintain shock level
• Clean the filter when pressure rises 20-25% above clean

This is the "maintain" part. You have to keep the chlorine at shock level. If it drops below, the algae starts growing again and you're back to square one.

Step 4: Brush, Brush, Brush

Algae forms a protective biofilm on your pool surfaces. Chlorine can't penetrate it until you break it up. Brush the entire pool at least twice a day during the SLAM - walls, floor, steps, corners, behind ladders, around lights, along the waterline. This is the step most people skip, and it's why their algae keeps coming back.

Step 5: Pass the Tests

You're done with the SLAM when all three conditions are met:

1. Water is clear - you can see the bottom of the deep end clearly
2. OCLT passed - test FC at sunset and again at sunrise. If you lost less than 1 ppm overnight, and CC is 0.5 or less, you're done.
3. CC at 0.5 or below - combined chlorine means there's still organic material being oxidized

If you fail any of these, keep going. Don't stop early - that's how algae comes back stronger.

How Long Does a SLAM Take?

For a light green pool: 2-3 days. For a dark green swamp: 5-7 days. For pools with very high CYA or severe neglect: longer, and you may need a partial drain first.

In Texas heat, algae grows fast. If you're dealing with a green pool right now, the sooner you start the SLAM, the easier it is. Don't wait - algae doubles every few hours in warm water.

Don't Want to Do It Yourself?

SLAMing a pool is hard work. It means brushing twice a day, testing every few hours, adding chlorine at 2 AM, and cleaning the filter repeatedly. If that's not how you want to spend your weekend, we get it. That's literally our job.

Our green pool recovery service includes the full SLAM process, all chemicals, filter cleaning, and we send you photo reports so you can watch your pool turn from green to crystal clear. Starting at $299. Get a free quote or call us at 682-399-2593.

SLAM Quick Reference

Need help with a green pool in Arlington or DFW? Se habla español. Call 682-399-2593 or get a free quote online.