How to Turn a Green Pool Blue: Complete Step-by-Step Guide

Tools & Supplies Needed

Find on Amazon: Taylor K-2006C Complete Pool Test Kit , Pool Brush for Algae Removal , Digital Pool Water Test Strips

First, Let's Diagnose Your Green Pool Problem

Your pool turned green because algae has taken over, which happens when chlorine levels drop too low or your water chemistry gets out of balance. Before we can fix it, we need to understand what type of green we're dealing with and test your current water chemistry.

Green pools typically fall into three categories: light green (you can still see the bottom), dark green (can't see past 12 inches deep), or black-green (completely opaque). The darker your water, the longer the treatment process will take.

Essential Water Testing and Diagnosis

Before adding any chemicals, test your water with a reliable test kit like the Taylor K-2006C. You need accurate readings for:

• Free Chlorine (FC) - likely at zero or very low
• pH - probably elevated due to algae photosynthesis
• Total Alkalinity (TA) - affects pH stability
• Cyanuric Acid (CYA) - determines how much chlorine you need
• Calcium Hardness (CH) - less critical for immediate treatment

If your CYA is above 80 ppm, you'll need to partially drain and refill your pool first, as high stabilizer levels make chlorine ineffective against algae.

The SLAM Method Solution

SLAM stands for Shock Level And Maintain, and it's the most effective method for clearing green pools. Here's how it works:

Calculate Your Shock Level

Your shock level depends on your CYA reading. Use this FC/CYA chart:

• CYA 30: FC shock level 12
• CYA 40: FC shock level 16
• CYA 50: FC shock level 20
• CYA 60: FC shock level 24
• CYA 70: FC shock level 28

Step-by-Step SLAM Process

1. Lower pH to 7.2 - Add muriatic acid if pH is above 7.6. Lower pH makes chlorine more effective.
2. Calculate chlorine needed - For every 10 ppm increase needed, add 1.3 gallons of 12.5% liquid chlorine per 10,000 gallons of pool water.
3. Add liquid chlorine - Pour around the perimeter with pump running. Never use granular shock or cal-hypo during SLAM.
4. Run filtration 24/7 - Your filter needs to remove dead algae constantly.
5. Test FC every 2-4 hours - Maintain shock level by adding more chlorine as needed.
6. Brush pool surfaces - Brush walls, steps, and floor twice daily to break up algae colonies.
7. Clean filter frequently - Backwash sand/DE filters or clean cartridge filters when pressure rises 10 psi.

What to Expect During Treatment

Don't panic if your pool doesn't clear immediately. Here's the typical progression:

Day 1-2: Water may get cloudier as dead algae particles circulate. This is normal and means the process is working.

Day 2-4: Water starts clearing from top down. You might see settling debris on the bottom.

Day 4-7: Water becomes increasingly clear. Continue SLAM until you can hold chlorine overnight.

The process is complete when your FC level stays stable for 8 hours without adding chlorine, indicating all algae is dead.

Critical Mistakes to Avoid

Don't use algaecide - It can interfere with chlorine and create foam. Proper chlorination kills algae more effectively.

Don't use flocculant initially - Wait until algae is dead before using floc to settle remaining particles.

Don't add clarifier too early - This can slow the process and clog your filter.

Don't swim during treatment - High chlorine levels are unsafe, and you'll interfere with the process.

Special Situations and Troubleshooting

If your pool isn't clearing after 5-7 days of proper SLAM:

• Check if your test kit is reading chlorine accurately - high CYA can interfere with DPD tests
• Verify you're maintaining true shock level 24/7
• Consider if your filter is adequate - you may need to rent a larger filter system
• Test for phosphates, which can fuel algae growth

For extremely dark green pools, consider hiring a service to drain and acid wash if SLAM isn't progressing after a week.

Final Water Balancing

Once your water is crystal clear and holding chlorine overnight:

1. Lower FC to normal levels (3-5 ppm based on your CYA)
2. Adjust pH to 7.4-7.6
3. Set TA to 80-120 ppm (60-80 for salt water pools)
4. Adjust calcium hardness to 250-350 ppm for plaster pools
5. Resume normal maintenance routine

The key to preventing future green pools is maintaining consistent chlorine levels and proper water balance. Test 2-3 times per week and address issues immediately.