Green Pool in Phoenix: Why It Happens and How It Clears

A pool turns green when algae grows faster than the chlorine can kill it. In the Phoenix area that usually follows a heat wave, a monsoon storm, or a few days of the pump not running. Hot water and strong sun burn off chlorine quickly, and storms blow in dust and debris that use up what's left.

Why it happens here

• Heat and sun. Water temperatures climb in summer, and sunlight breaks down chlorine fast. A pool that held fine in April can lose most of its chlorine in a day or two in July.
• Monsoon storms. Dust, leaves and rain all add load to the water at once.
• Pump or filter problems. If the water isn't moving or the filter is clogged, algae gets a head start. A green pool is often a pump problem first. See pool pump not working.
• Hard water and high stabilizer. Phoenix water is hard, and high cyanuric acid (stabilizer) makes chlorine work more slowly. A water test shows both.

What you can try yourself

1. Make sure the pump runs and the filter is clean.
2. Test the water, or take a sample to a pool store for a free test.
3. Brush the walls and floor so the chlorine can reach the algae.
4. Shock the pool following the product label, usually in the evening so the sun doesn't burn it off.
5. Run the pump around the clock and clean the filter again as it clears.

If the water turns cloudy blue after a day or two, that's progress. If it stays green after a few days, or you can't see the floor at all, a pool company can usually clear it faster than repeated rounds of shock.

When to call a pool company

Call if the pool is too dark to see the floor, if it keeps turning green within a week of clearing, or if the stabilizer reading is very high. A high stabilizer level often means draining part of the water, and draining a pool in the Arizona heat can damage the plaster. That's a job for someone who has done it before.

Some pool owners in the Valley skip the fight and put the pool on weekly service. Our city pages list local pool companies by Google rating: Phoenix, Scottsdale, Mesa, Gilbert, Chandler, Tempe, Glendale and Peoria.