You walked outside after the storm and now your pool is green. Why does this happen every year? The monsoon hits and somehow the pool that looked fine yesterday is now the color of a swamp. You're not sure what went wrong.
At Shasta, we've been servicing Arizona pools since 1966. Our Weekly Pool Care and Service team responds to more green pool calls during monsoon season than any other time of year.
This article explains why your pool turns green after a monsoon storm. Next, what your pool chemistry is doing during the storm, and what you can do to stop it from happening.
Table of Contents
- Why Does a Monsoon Turn a Pool Green So Fast?
- Why Rainwater and Haboob Dust Pull Your pH in Opposite Directions
- Why Does My Neighbor's Pool Stay Blue After the Same Storm?
- Why Did My Pool Turn Green Overnight After the Storm?
- Your Pool Was Already Vulnerable Before the Monsoon Hit
Why Does a Monsoon Turn a Pool Green So Fast?
Most of the time, the monsoon didn't actually cause your pool to go green. Your pool was ready and the storm pushed your pool out balance and a green pool is the result.
At Shasta, we see it constantly monsoon time of year. The conditions for a green pool were already building before the storm hit. First, the filter was running short hours left over from winter settings. Then the chlorine tabs weren't keeping up with Arizona's heat. Now, the pH is rising and making chlorine less and less effective. The monsoon dumps a wall of dust and debris into the pool, and overwhelms the system.
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Dumps alkaline dust and debris that drives pH even higher
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Overloads a filter that was already clogged
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Adds phosphates that are the nutrient for algae
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Dilutes chlorine levels at the exact moment demand spikes
Green Pool Perfect Storm
"Every time we walk in it feels like a perfect storm that happened for the customer. One they didn't get their cartridges cleaned or filter cleaned or backwashed. Then you get clogged up with more debris from the wind and the monsoon or the dust storms that roll through. And we just got a lot of dust so it's going to get extra clogged up and then you're not able to even maintain those chems once that happens." — Brock Falk, Field Manager, Weekly Pool Care & Service/Repair, Shasta Pools
What Does Monsoon Rain Actually Do to Your Pool Chemistry?
A monsoon adds rain, dust, debris, pollen, and airborne particles. Each one hits your water chemistry differently. Some push your pH up. Some pull it down. None of it is neutral, and none of it is predictable. This is what makes monsoon season harder on Arizona pools.
Why Rainwater and Haboob Dust Pull Your pH in Opposite Directions
Rainwater is naturally acidic. When it falls into your pool it lowers pH. A sudden pH drop destabilizes your alkalinity. Now, your pool water chemistry is unstable. Once alkalinity is disrupted, chlorine can't do its job consistently.
With the haboob, the dust walls are loaded with fine alkaline particles, soil, minerals, and organic matter. That dust lands in your pool and pushes pH up. Dust storms carry fine particulate matter and create an environment where bacteria thrive.
So, in a single storm event you can have rain pulling your pH down and dust pushing it up. The result is a pool chemistry system that's been knocked off its foundation and is now swinging between two extremes.
Arizona Water Naturally High pH
"Our natural water is pretty high. It's usually around an 8.0. So that means your pool is always driving up. Plus with the wind and aeration and all that, your pH kind of climbs, which makes your chlorine non-effective. A low chlorine with the high pH, your chlorine is not doing its job. So you got to get that pH down for that chlorine to be effective." — Brock Falk, Field Manager, Weekly Pool Care & Service/Repair, Shasta Pools
Why Does My Neighbor's Pool Stay Blue After the Same Storm?
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The same storm hits the same street. Your neighbor's pool looks great while yours is all green.
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Source water — each house has different baseline pH, alkalinity, or even salt content
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Filter age and maintenance history — a well-maintained filter handles storms better
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Sun and wind exposure — more direct exposure means faster chemical breakdown
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Landscaping and tree cover — more organic debris means more chlorine demand
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Pool Usage — pets, kids, and daily use differences
No Single Answer
"I tell customers all the time, your next door neighbor can have the identical backyard as you, and it'll take totally different chemicals to maintain that pool. I mean they can be in the ballpark, but they will be different. There's so many factors." — Brock Falk, Field Manager, Weekly Pool Care & Service/Repair, Shasta Pools
How Source Water Differences Affect Pool Chemistry
The water coming out of your auto-fill line can have a different baseline pH and alkalinity. A lot of homeowners in the Phoenix area also have salt already present in their source water, which changes how their pool behaves entirely.
Source water, which sounds funny, but your actual tap water. The hose bib that supplies your auto fill, get that tested, find out what your standard pH is, alkalinity. You may have chlorine in your water. You may have a registered amount or even you might have salt in your water. A lot of people in Phoenix do have salt in their water.
The Role Landscaping, Pets, and Usage Play in Pool Chemistry
The backyard around the pool matters as much as the pool itself. A yard with heavy tree cover drops more organic debris into the water. Now, your pool consumes chlorine as it breaks down. A pool that gets used daily by kids or pets introduces more bather load. Sunscreen and oils place additional demand on your sanitizer.
So, your pool goes green after a monsoon and your neighbor's doesn't. It's usually a combination of source water, filtration history, and everyday backyard factors that were already different.
Why Did My Pool Turn Green Overnight After the Storm?
The pool looked fine yesterday. This morning it's green.
Algae is a living organism. It reproduces faster in warm water and Arizona pool water in July and August often hits above 85 degrees. A pool that looked clear at sunset can show the first hint of cloudiness by morning and be fully green by the following afternoon. The algae was likely present in small and invisible amounts the whole time. Once it gets the conditions it needs, it stops being invisible almost immediately.
My Pool Went Green
"Absolutely. We get all different calls this time of year. Now majority of our calls are my pool went green. I need a one time service or one time cleaning. A lot of the come to the rescue calls happen now while we're still growing." — Brock Falk, Field Manager, Weekly Pool Care & Service/Repair, Shasta Pools
The Four Conditions That Turn a Pool Green in Under 24 Hours
A pool goes green overnight usually takes a combination of the same four conditions stacking on top of each other.
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Low chlorine — not enough sanitizer
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High pH — chlorine not working
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Poor circulation — a clogged filter can't distribute chemicals
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Elevated phosphates — fresh fuel for algae
Your Pool Was Already Vulnerable Before the Monsoon Hit
Your pool didn't turn green because of one bad monsoon. It turned green because the conditions were already working against it. Your filter needed cleaning or chlorine wasn't keeping up with Arizona heat. Maybe your pH was climbing higher than it should, and then a wall of phosphate-loaded dust gave algae everything it needed.
The storm gets blamed every time. The truth is it just exposed what was already happening underneath. Basically, it means this isn't a problem you have to accept as inevitable every monsoon season. The pools that come through are prepped. Clean filter, correct pump run time, chlorine that matches the heat, and pH that's in range.
If your pool is green right now, the fix can be fast. Most monsoon-related green pools clear up in a day once circulation and chemistry are corrected. If you want to get ahead of the next storm, prep your pool now.
References
Shastapoolsupply.com How to Prepare Your Pool for Monsoon Season
Bluesquaremfg.com Monsoon Maintenance
Orendatech.com Phosphates in Pools
