Why Is My Pool Green? Causes & How to Fix It Fast
You wake up, look out at your pool, and... it's green. Don't panic. A green pool is one of the most common problems I see, and in most cases, it can be fixed within 3-5 days. Here's what's happening and how to restore your crystal-clear water.
What Makes a Pool Turn Green?
The short answer: algae. Algae spores are everywhere—in the air, on your skin, in rain. When conditions are right, they bloom rapidly and turn your pool into a swamp.
Common Causes of Algae Blooms
- Low chlorine levels — The #1 cause. Chlorine kills algae; without it, algae thrives
- Poor circulation — Pump not running enough or dead spots in the pool
- High pH — Chlorine becomes ineffective above 7.8 pH
- Warm water — Algae grows fastest in 75-85°F water
- Heavy rain — Dilutes chemicals and introduces contaminants
- Neglected filter — Dirty filters can't remove algae particles
Types of Pool Algae
Green Algae (Most Common)
Floats in water, makes it cloudy green. Easiest to treat.
Yellow/Mustard Algae
Clings to walls in shady areas. Harder to kill, often comes back.
Black Algae
Roots into plaster/concrete. Very difficult to eliminate completely.
How to Fix a Green Pool
Severity Check: Can you see the bottom? If yes, treatment is straightforward. If no, you may need professional help or drain/refill.
Step-by-Step Treatment
- Test and balance pH first
Bring pH to 7.2-7.4. Shock won't work effectively at high pH. - Brush everything
Walls, floor, steps, ladders. This breaks up algae and exposes it to chemicals. - Triple or quadruple shock
Use 3-4 lbs of calcium hypochlorite per 10,000 gallons. Don't be shy. - Run pump 24/7
Keep water circulating until clear. This could take 3-5 days. - Clean filter frequently
Backwash or clean cartridge every 12-24 hours during treatment. - Brush and shock again if needed
Repeat daily until water clears. - Vacuum dead algae
Once water is blue but cloudy, vacuum to waste (bypass filter).
How Long Does It Take?
- Light green: 1-2 days
- Medium green: 3-4 days
- Dark green/black: 5-7 days or drain and refill
Prevention: Keep It From Happening Again
- Maintain chlorine at 1-3 ppm at all times
- Run pump 8-12 hours daily in summer
- Test water weekly (twice weekly in peak summer)
- Shock weekly during swim season
- Clean filter monthly
- Brush walls weekly
Green Pool Emergency?
I offer fast green pool cleanup service throughout the DFW area. Most pools are swim-ready within 5-7 days. Get a quote and I'll have your pool back to crystal clear.