It happens fast. The pool was clear on Friday, a storm rolls through Saturday afternoon, and by Sunday morning the water has gone from blue to a cloudy green that seems to have come out of nowhere. Nothing broke. What happened is a fairly predictable chain of events, and if you work through it in the right order the pool comes back much faster than if you start throwing chemicals at it.
What the Storm Actually Did
Three things happen at once, and each one makes the others worse.
First, dilution. A heavy Gulf Coast storm can drop several inches into an open pool in an hour. Rainwater carries no chlorine, so every gallon that lands in the pool waters down the sanitizer that was protecting it. It is also acidic, so it drags pH and total alkalinity down with it and pushes the water out of the range where chlorine works efficiently in the first place.
Second, organic load. Wind and runoff carry in everything that was sitting on the deck, the roof, the screen and the landscaping. Leaves, pine needles, pollen, dirt, mulch, lawn fertilizer, bird droppings. All of it consumes chlorine as it breaks down, and fertilizer in particular is packed with phosphates and nitrates that algae feed on directly.
Third, and this is the one people forget, the power. If the pump lost power for even a few hours, circulation stopped. Water that is not moving is not being filtered or sanitized, and in eighty-something degree water that is all the opening algae needs. A pool with zero free chlorine and no circulation in July can visibly bloom in under twenty-four hours.
Do Not Drain It
This is the first instinct for a lot of owners and it is the wrong one. Draining a pool in Florida is genuinely dangerous to the pool itself. Our water table is high, especially after the exact kind of storm that turned the water green, and an empty shell can float, crack or shift in the ground. That is a five-figure problem replacing a green-water problem that costs a fraction as much to fix chemically. Almost every green pool on this coast can be recovered without emptying it.
The Right Order of Operations
1. Get the debris out first
Before any chemical goes in, net the surface and the bottom and empty both the skimmer and pump baskets. Every leaf sitting in that water is actively eating the chlorine you are about to add. Skipping this step is the most common reason a shock treatment seems to do nothing: it did work, it just got consumed by the debris instead of the algae.
2. Clean the filter
The filter is about to do the heaviest work of its year, and a storm has usually just loaded it up. Pull and rinse the cartridges, or backwash and recharge a DE filter. Check the pressure gauge against its clean baseline. A filter that is already restricted cannot clear a green pool no matter how perfect the chemistry is, because the dead algae has nowhere to go.
3. Test before you dose
Test pH, total alkalinity, free chlorine and cyanuric acid. Do not skip to shocking. Chlorine loses a large share of its killing power at high pH, so shocking a pool sitting at 8.0 wastes most of what you put in. Bring pH into the 7.2 to 7.4 range first, and check that alkalinity is somewhere around 80 to 120 ppm so the pH will actually hold there.
Cyanuric acid matters here too. If the stabilizer level has climbed far above roughly 100 ppm, chlorine becomes so bound up that it struggles to work at any dose. If that is what the test shows, no amount of shock will fix the pool. The water has to be partially diluted first.
4. Shock it properly, and at the right time of day
Green water needs a real shock dose, not a maintenance dose. Under-shocking is the single most common mistake we see: it kills some of the algae, the pool turns a murky grey-green, and then it stalls and comes right back. Follow the product's green-pool dosage rather than its weekly dosage.
Do it at dusk. Sunlight destroys unstabilized chlorine within hours, so shocking at noon in July throws away a good portion of what you just paid for. Shocking in the evening gives it the whole night to work.
5. Run the pump continuously
Twenty-four hours a day until the pool is clear, not the usual eight. Circulation is what carries chlorine to the algae and carries dead algae to the filter. This is not the week to save on the power bill, and it is the step most likely to be quietly skipped.
6. Brush, then brush again
Brush the walls, steps, waterline and especially the shaded corners and behind the ladder. Algae anchors to surfaces and forms a film that shields the colony underneath from chlorine. Brushing breaks that film open and exposes it. Brush daily until the water clears, and expect to clean the filter more than once during the process as it loads up with dead algae.
What Recovery Should Look Like
Green turning to cloudy grey or milky white is not a failure, it is exactly what you want to see. It means the algae is dead and suspended in the water, and now it is a filtration problem rather than a chemistry problem. Keep the pump running and the filter clean and it will clear from there.
A pool that went green two days ago typically comes back in two to four days. One that has been sitting green for weeks, where the bottom is not visible, can take a week or more and will go through several filter cleanings. Water that stays green after a proper shock and forty-eight hours of full circulation is telling you something else is wrong, usually stabilizer that is far too high or a filter that is not actually moving water.
When to Stop and Call Someone
Call if the pool is still green after a correct shock and two full days of circulation, if you cannot get pH to hold anywhere, if the water has gone a mustard or brownish-yellow rather than green, or if you are pouring money into chemicals without a test kit telling you what the water actually needs. Mustard algae in particular is chlorine-resistant and needs a different treatment than a standard green bloom.
The honest truth is that most green pools are preventable. The pools that go green after a storm are almost always the ones that were already running on thin chlorine before it rained. A pool that goes into a storm with correct chemistry and a clean filter usually comes out of it cloudy for a day and then clears on its own.
If you would rather not do any of the above, that is what we handle. WittCo Pools services pools across Destin, Miramar Beach, Santa Rosa Beach, Sandestin, Fort Walton Beach, Navarre and Crestview. Call (850) 660-3394 or request a free quote.
