A green pool can make your whole backyard feel like a disaster zone. One week the water looks fine, then suddenly it turns cloudy, swampy, green, or even dark enough that you cannot see the floor. The good news is that most green pools can be fixed. The bad news is that many pool owners waste time and money because they treat the color instead of the cause.
Green pool water is usually caused by algae, but the reason algae takes over is almost always bigger than one missing chemical. Low sanitizer, poor circulation, weak filtration, high phosphates, bad water balance, heavy debris, warm weather, and inaccurate testing can all work together to create the perfect algae bloom.
Why Pool Water Turns Green
Pool water usually turns green when algae starts growing faster than your sanitizer can control it. That can happen after heavy rain, during hot weather, after a pool opening, when the pump is not running long enough, or when the filter is too dirty to keep up.
Low chlorine is one of the most common reasons a pool turns green, but it is not the only one. A pool can have chlorine in the water and still struggle if the pH is too high, the stabilizer level is off, the filter is clogged, the pump is weak, or the salt system is not producing enough sanitizer.
Common causes include:
- Low free chlorine or poor sanitizer performance
- High pH that makes chlorine less effective
- High cyanuric acid (stabilizer) reducing chlorine effectiveness
- Dirty filter cartridges, old sand, or clogged DE grids
- Weak circulation from pump issues or blocked returns
- Heavy rain, pollen, and organic debris
- High phosphates (algae food source)
Step 1: Test the Water Before Adding More Chemicals
The first step in fixing a green pool is accurate testing. Test strips can be useful for quick checks, but when a pool is chemically unstable, you need better information.
For dependable readings, we recommend Taylor Water Technologies test kits or LaMotte test kits. The Taylor K-2006C-8 Service Complete Kit is a pro-style option for serious pool owners.
Step 2: Remove Debris and Brush the Pool
Leaves, pollen, and dirt use up chlorine quickly. Skim the surface and vacuum heavy debris. Brushing is critical because algae clings to walls and corners. If you don't brush, the sanitizer can't reach the algae effectively.
Step 3: Balance pH and Alkalinity
Shock works best when the water is properly balanced. If pH is too high, chlorine becomes less effective. Adjust these before adding shock to ensure your chemicals work as intended.
Step 4: Shock the Pool to Kill Active Algae
Shock is your primary weapon. Follow the label for dosage and shock in the evening to prevent sunlight from burning off the chlorine. After shocking, the water may turn cloudy blue or gray—this is a sign the algae is dying.
Step 5: Run the Filter and Clean It Often
The filter must remove the dead algae. Run your pump continuously and watch the pressure gauge. You may need to backwash or rinse cartridges multiple times during the clearing process.
Step 6: Use Clarifier or Flocculant
When to Use Lo-Chlor Miraclear Blue Clarifier
Lo-Chlor Miraclear Blue Clarifier is perfect for hazy or dull water. It binds tiny particles so the filter can catch them.
When to Use Lo-Chlor Knockdown Flocculant
Lo-Chlor Knockdown Flocculant is for severe cloudiness. It drops dead algae to the floor for vacuum removal.
Step 7: Remove Phosphates
Phosphates are algae food. Once the bloom is under control, use Lo-Chlor Lo-Phos Max to reduce nutrient levels and prevent future blooms.
Step 8: Prevent Future Blooms
Prevention is easier than the cure. Use Lo-Chlor 90-Day Algicide for long-lasting protection and maintain a regular testing routine.
Green Pool Product Guide: The Right Fix
Frequently Asked Questions
Get the Right Fix from Aqua Terra Backyard
Don't just chase the color—treat the cause. We carry everything you need from Lo-Chlor treatments to Taylor test kits.