Quick Answer

When a pool turns green overnight, it is almost always caused by a sudden drop in chlorine combined with fast-growing algae. Warm temperatures, heavy pool use, rainstorms, and poor circulation can allow algae to bloom extremely fast — sometimes in just a few hours. The good news is that green water can usually be cleared within 24–48 hours with the right treatment.

Quick Green Pool Emergency Checklist

If your pool turns green suddenly, do this immediately:

• Test chlorine and pH

• Raise chlorine to shock level

• Brush the entire pool

• Clean or backwash the filter

• Run pump continuously for 24–48 hours

• Re-test and rebalance water

What Causes a Pool to Turn Green Overnight?

1. Low Chlorine Levels

If chlorine drops below 1–2 ppm, algae can multiply rapidly — especially in warm weather.

2. Heat & Sun Exposure

High heat and UV rays burn off chlorine faster, especially without enough stabilizer (CYA).

3. Rainstorms & Debris

Rain adds contaminants and washes in debris that consume chlorine quickly.

4. Poor Circulation or Dirty Filter

If water is not circulating properly, algae can bloom in stagnant areas.

5. Heavy Pool Use

Multiple swimmers add sunscreen, sweat, and oils that rapidly deplete sanitizer.

How to Fix a Green Pool Fast (Step-by-Step)

1. Test chlorine and pH

2. Adjust pH to 7.2–7.4

3. Add heavy shock dose

4. Brush walls, steps, and floor

5. Run pump 24–48 hours nonstop

6. Clean filter daily until water clears

7. Vacuum dead algae after it settles

How Long Does It Take to Clear a Green Pool?

• Light green: 24 hours

• Medium green: 24–48 hours

• Dark green / swamp: 2–4 days with heavy treatment

How to Prevent a Pool from Turning Green

• Maintain chlorine 2–4 ppm

• Keep stabilizer between 30–50 ppm

• Run pump 6–10 hours daily

• Brush weekly

• Shock after heavy use or storms

When to Call a Pool Professional for a Green Pool

Call a pro if:

• Green water lasts more than 48 hours

• Algae keeps returning

• Filter pressure stays high

• Water won’t hold chlorine

• Pool turns green repeatedly

Green Pool Cleanup in Peoria, AZ

If you’re in Peoria or the West Valley, Triton Pools specializes in fast green-to-clean pool transformations.

• 4.9★ rating with 600+ reviews

• Emergency algae treatment

• Full water chemistry recovery

• Filter cleanings and equipment checks

Book your green pool cleanup with Triton Pools today.

FAQ: Green Pool Water

Can a pool really turn green overnight?
Yes. In hot weather with low chlorine, algae can bloom within hours.

Is it safe to swim in green pool water?
No. Green pools contain bacteria and algae that can cause illness.

Why does my pool turn green even when I use chlorine?
This usually indicates incorrect dosing, poor circulation, or high stabilizer.

Should I drain my green pool?
Almost never. Most green pools can be corrected with proper chemical treatment.