You've come home from a vacation to find your pool has turned green. In Phoenix summer heat, this can happen in as little as 3–5 days without active chemistry maintenance. The green color comes from algae bloom — typically green algae, though mustard algae (yellow-green) and black algae (dark spots) are also common in Valley pools.
The good news: a green pool is almost always recoverable without draining. The bad news: recovering it correctly takes 3–7 days and a specific sequence of steps. Do it wrong and you can bleach a plaster surface, damage equipment, or have the algae return within days.
Why Your Pool Turned Green
Algae needs three things to bloom: warm water, sunlight, and inadequate sanitizer. When free chlorine drops below 1 ppm in 100°F Phoenix pool water, algae can establish within hours. The most common vacation scenarios: the automatic chemical feeder ran out, the pump timer failed and the pump stopped running, or a dust storm overwhelmed the chemistry before it could recover.
The Right Recovery Sequence
- Test the water first. Don't add chemicals until you know your baseline pH, alkalinity, and stabilizer levels. A shock treatment applied to a pool with severely imbalanced pH won't work effectively.
- Adjust pH to 7.2–7.4. Chlorine is most effective in this range. If pH is above 7.8, even a heavy shock dose will be largely ineffective.
- Brush the entire pool surface. Physically disturb the algae on walls, steps, and floor before adding chemicals. Algae has a protective biofilm — brushing breaks it and allows chlorine to penetrate.
- Shock to 30 ppm free chlorine. This sounds high, but green pool recovery requires maintaining elevated chlorine long enough to kill all algae. Use calcium hypochlorite shock, not liquid chlorine, for severe cases. Add at dusk to prevent UV degradation.
- Run the filter continuously. 24 hours a day until the pool clears. The filter removes dead algae. Clean or backwash the filter daily during recovery.
- Add a clarifier. After shocking, a clarifier helps dead algae particles clump together so the filter can capture them more efficiently.
⚠️ Don't drain a plaster pool without professional assessment
Draining a plaster or Pebble Tec pool in Phoenix summer heat without proper precautions can cause bowing or cracking of the shell due to hydrostatic pressure and thermal expansion. Always consult a pool professional before draining. In most cases, a proper green-to-clean treatment is faster and cheaper than a drain-and-refill anyway.
How to Prevent It Next Time
- Install an automatic chlorine feeder (erosion feeder or salt system) if you don't have one
- Set the pool pump to run 10–12 hours/day minimum in summer
- Maintain stabilizer (cyanuric acid) at 60–80 ppm to protect chlorine from UV
- Ask your pool service provider about vacation chemical treatments before you leave
If your pool has already turned green, AquaCare handles green-to-clean recovery throughout the Phoenix metro. We typically have the pool swim-ready within 5–7 days with proper treatment.