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Pebble & PalmPool Co.

Why did my pool turn green overnight?

The call comes every July, usually before 8 AM: “It was perfect yesterday. I’m not exaggerating — yesterday. Now it looks like a smoothie.”

We believe you. Overnight green is real, it’s a monsoon specialty, and it isn’t your fault. Here’s what actually happened in those twelve hours — and exactly how to undo it.

What the storm actually dumps in your pool

A good haboob doesn’t just rearrange your patio furniture. The dust wall is a delivery system carrying three things your pool fears:

  • Phosphates — algae groceries. Desert dust is loaded with them. One storm can push a pool from “starved” to “all-you-can-eat” in an evening.
  • Organic debris — leaves, pollen, bugs. Everything organic consumes chlorine as it breaks down, draining your sanitizer reserve overnight.
  • Live algae spores. They’re always drifting around outside. The storm just delivers a few million at once, pre-fed.

The chain reaction, hour by hour

Around dinner time, the storm hits and the buffet opens. Your chlorine starts oxidizing the new debris immediately — that’s its job — but every milligram spent on dust is a milligram not guarding against algae.

By midnight, free chlorine has dropped near zero. Water is still warm — 88°, maybe 90° — which is algae’s favorite incubator. With food, warmth, and no sheriff in town, spores begin doubling roughly every three to six hours.

By sunrise: four or five doubling cycles. That’s the smoothie.

“A monsoon green-up isn’t a neglect problem. It’s an ambush. The fix is fast if you move within 48 hours.”

The 48-hour fix

Move quickly and this is a weekend story, not a week-long one:

  • Net the big stuff first. Every frond you remove is chlorine you don’t have to spend. Empty both baskets while you’re at it.
  • Brush everything. Walls, steps, tile line. Algae anchored to surfaces shrugs off chemicals; suspended algae dies fast.
  • Shock hard, at dusk. A proper shock dose (not one lonely bag) after sundown, so the sun doesn’t burn it off before it works.
  • Run the pump 24/7 until the water clears. Filtration is half the cure — clean the filter when pressure rises.
  • Re-test in the morning. If chlorine held overnight, you’ve won; now it’s just filtering. If it vanished again, the bloom is still eating — repeat the dose.
Weekly members: skip this whole article.

Storm sweeps run automatically after every major monsoon, and member pools that turn between visits get rescued free. That’s the whole point of the plan.

When to wave the white flag

If the water’s been green for more than a few days, if you can’t see the first step, or if the filter was already struggling — the DIY math stops working. A professional green-to-clean rescue includes the filter rehab and shock cycles that hardware-store kits can’t match, and it comes with a guaranteed day count.

Either way: don’t drain a green pool to “start over.” In our heat, an empty pool can pop out of the ground or destroy its finish in a day. Green water is fixable. A floated shell is not.

Marcus Webb · Lead Service Tech

Eleven years on Valley routes and a personal record of 41 storm sweeps in one July week. Writes the way he services pools: thoroughly, with photos.

Storm season is coming. Be the ready house.

Weekly members get automatic storm sweeps and free green-pool rescues. Just saying.

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