A green pool is one of the most common — and most fixable — problems a pool owner faces. The culprit is almost always algae, which thrives when chlorine levels drop too low. The good news: you don't need to drain the pool or call a pro. With the right products and a little patience, you can restore crystal-clear water in 3–5 days.
Why Is My Pool Green?
Green pool water is caused by algae growth. Algae blooms when free chlorine drops below 1 ppm, which can happen after heavy rain, extended periods without shocking, or high temperatures that accelerate chlorine consumption. The shade of green tells you how severe the problem is — light green means early-stage algae, dark green or black-green means a heavy bloom.
What You'll Need
- Pool shock (calcium hypochlorite, 68% or higher)
- Algaecide
- Pool brush
- Test kit or test strips
- Clarifier (optional, for faster clearing)
Step 1: Test Your Water
Before adding anything, test your pH and alkalinity. Shock is most effective when pH is between 7.2 and 7.4. If your pH is too high, add pH decreaser first — otherwise the shock won't work properly.
Step 2: Brush the Walls and Floor
Use a stiff pool brush to scrub all surfaces — walls, floor, steps, and behind ladders. This breaks up the algae biofilm and exposes it to the chemicals you're about to add.
Step 3: Triple-Shock the Pool
For a green pool, standard dosing isn't enough. Use triple the normal shock dose: 3 lbs per 10,000 gallons. Add the shock directly to the water around the perimeter of the pool in the evening. Never add shock through the skimmer.
Step 4: Add Algaecide
After shocking, add a quality algaecide to prevent regrowth. Follow the label dosing instructions based on your pool volume.
Step 5: Run the Filter Continuously
Run your pump and filter 24/7 until the water clears. Backwash or clean your filter every 8–12 hours — a green pool will clog a filter fast.
Step 6: Retest and Repeat if Needed
After 24 hours, retest your water. If it's still green, shock again at double dose. Most pools clear within 3–5 days with consistent treatment.