A green pool recovery runs in five stages, and a reading ends each one. Test cyanuric acid (CYA), sold as stabilizer, first; brush and shock at a dose calculated from it; and use the overnight chlorine loss test to confirm the kill. Then filter until the water clears, rebalance, and write down the cause.
CYA comes first because it decides whether the shock works at all. The CDC’s home pool guidance warns that “disinfection times are longer in the presence of cyanuric acid.” A tablet-fed pool that has gone green often carries a lot of it, so shock dosed without that reading is how recoveries stall. The readings below let you hold any company, us included, to a written standard.
The numbers are the thresholds we work to and the durations we see on a typical 15,000 to 20,000 gallon Collin County pool in summer, not a transcript of one customer’s pool. A real job deviates: some clear in three days, some take nine. Where a stage commonly runs long, we say so rather than quoting the best case.
Day zero: the readings before anything is added
On day zero, nothing goes in the pool until the water has been tested with a drop kit or a photometer rather than strips. Strips are unreliable at the extremes, and a green pool is nothing but extremes.
| Test | Why it decides the plan | What a green pool commonly reads |
|---|---|---|
| Cyanuric acid | Sets the entire shock dose. This is the number that determines the job | 60 to 120 ppm, often higher on a tablet-fed pool |
| Free chlorine | Confirms the sanitizer is absent | 0.0 to 0.5 ppm |
| Combined chloramines | High combined means organic load, not just algae | Often present |
| pH | Chlorine is less effective at high pH | 7.8 to 8.4, usually high |
| Total alkalinity | Decides whether pH will hold once corrected | Variable |
| Calcium hardness | Affects whether we can safely use cal hypo to shock | Frequently high here |
| Phosphate | Algae food. High phosphate means it comes back | Often elevated after storms |
| Filter pressure at startup | The baseline every later reading is compared to | Recorded, not judged |
We photograph the pool from a fixed corner on day zero and from the same spot every subsequent visit. Recovery is gradual and hard to judge by eye, and two photographs a day apart settle arguments that a memory cannot.
The cyanuric acid decision
The CYA decision is the fork in the road, and in our experience the step most often skipped. Chlorine’s effectiveness is governed by its ratio to CYA, not by its absolute reading. Shocking a pool at 100 ppm CYA to the same chlorine level that clears a pool at 40 ppm does little, and the owner concludes that shock does not work.
So the first decision is whether to dilute before treating. Above roughly 80 to 100 ppm, a partial drain and refill comes first, because the alternative is a shock dose so large that it is both expensive and hard on the surface. How much water that takes is worked out in the cyanuric acid guide, and how to do it safely in this soil is in draining a pool in Collin County clay.
Day one: mechanical work, then the first dose
Chemistry goes in last on day one, after several hours of work that has nothing to do with chemicals. Dosing a pool full of leaves is dosing the leaves.
| Task | Typical time | Done when |
|---|---|---|
| Net out leaves and heavy debris | 20 to 60 minutes | Nothing large left floating or on the steps |
| Empty skimmer and pump baskets | 5 minutes | Both clear, lids reseated |
| Check the filter and clean if loaded | 20 to 45 minutes | Pressure back near baseline |
| Confirm the pump and returns are circulating | 10 minutes | Flow visible at every return |
| Brush every surface | 30 to 60 minutes | Walls, floor, steps, behind the ladder, waterline. This is the step that decides how well the shock works |
| Correct pH down toward 7.2 | Dose and circulate | pH reads 7.2 to 7.4 before shocking |
| Shock, dose calculated from the CYA reading | 15 minutes to dose | Full dose in, pump running |
| Run the pump continuously | Overnight, not on a timer | It does not stop until the pool is clear |
Brushing is not optional
Algae holds to surfaces behind a protective layer. Chlorine reaches the water first and the attached colony last, which is why an unbrushed pool can be dosed to 20 ppm and still be green in the morning while the chlorine reading collapses. Brushing breaks the layer and puts the organism into the water where the chlorine is. On a heavy recovery we brush at every visit, not only the first.
Day two: the overnight chlorine loss test
The overnight chlorine loss test tells you whether anything is working, and few owners outside the trade run it.
Test free chlorine at dusk and record it. Test again at first light, before the sun is on the water. Sunlight destroys chlorine, so testing overnight removes that variable and leaves one explanation for a loss: something in the water is consuming it.
The loss test has three results. More than 1 ppm lost means living algae or a significant organic load is still in there: re-dose to shock level, brush again, and hold. One ppm or less means the kill is complete, and it is the moment to stop adding chlorine entirely. Chlorine gone altogether by morning means the dose was too small for the CYA level, or the load is heavier than it looked. The answer is to recheck CYA and recalculate rather than to repeat the same dose harder.
Passing the loss test is the milestone that changes the job. Before it, you are still killing. After it, adding more chlorine accomplishes nothing and the remaining work is entirely mechanical.
What day two usually looks like
On day two, green usually becomes gray, cloudy, or milky blue. Owners frequently read this as the treatment having failed, because the pool looks worse in photographs than it did when it was a clear green. It has not failed. Gray is dead algae in suspension, and suspension is where the filter can finally reach it.
Days two to five: filtration, which is the long part
Filtration is the long part of a recovery: killing algae takes a day, and removing it takes most of the week. This stage is limited by how much water passes through your filter and how fine that filter is, which is why filter type and pump run time matter more here than any product does.
| Reading | Target | What it tells us |
|---|---|---|
| Free chlorine | Held at shock level until the loss test passes, then 3 to 5 ppm | Whether anything is regrowing |
| Filter pressure | Clean when 8 to 10 psi above baseline | How much dead algae has been captured. Rising fast is good news |
| Water clarity by depth | Main drain visible, then sharp-edged | The actual progress measure |
| pH | 7.2 to 7.6 | Drifts during a recovery, needs watching |
| Pump hours | Continuous, 24 hours | Not a timer schedule. This is the stage that ends sooner with more run time |
On a cartridge filter, expect to pull and clean the element more than once during a heavy recovery, sometimes daily. On sand or DE (diatomaceous earth), expect repeated backwashing, and expect to be adding water back. A recovery is one of the heaviest loads a residential filter carries, so doing this stage properly includes telling the customer their filter may need attention. Costs are in what filter cleaning costs.
The flashlight test
At dusk, shine a light down through the water from the deck. Fine suspended particles scatter the beam and make it visible in the water column. As the pool clears, the beam sharpens to a defined line. It is a more sensitive test of clarity than looking at the main drain and it will tell you a day earlier whether progress has stalled.
When day three does not go to plan
A stalled recovery usually has one of a short list of causes. If the pool is not visibly better by the third morning, we work through this in order rather than adding more chemicals.
- Retest CYA from a fresh sample. The most common cause, in our experience: the dose was calculated against a number that was wrong or has since moved.
- Confirm the pump ran all night. A timer, an automation schedule, or a breaker that tripped in the dark undoes the whole previous day, and it leaves no evidence in the morning.
- Check filter pressure, and clean it if it is high. A blinded filter circulates without filtering, which looks identical from the deck.
- Watch the returns for real flow. A clogged impeller or a suction-side air leak halves the turnover while the pump sounds normal, and it is a commoner cause of a stall than people expect. The symptoms are in air bubbles at the returns.
- Retest pH. If it climbed, the chlorine sitting in the water is less active than the reading suggests.
- Look hard at the color and the surfaces. Mustard clinging in shade and black algae rooted in plaster are different organisms with longer treatments, not a green pool recovery going slowly. Pool algae types identified covers what each one takes.
- Test phosphates. A heavy nutrient load can feed regrowth about as fast as the chlorine kills it.
Closing the job
Closing a recovery means getting the pool back to a state that will hold, not only to blue water. Five things are on that list.
- Clean the filter one final time. It is holding everything that came out of the pool. Leaving it loaded hands the customer a problem in two weeks.
- Vacuum the settled fines. Whatever the filter did not catch is on the floor as a gray film, and it goes to waste rather than back through the filter if the valve allows.
- Rebalance fully. Alkalinity first, then pH, then calcium, then CYA if the recovery involved diluting. In that order, for the reasons in the water chemistry guide.
- Deal with phosphates if they are high. Otherwise the same pool goes green again in a month and everybody blames the chlorine.
- Write down why it happened. A failed pump, a two week vacation, a storm, a tablet feeder that ran empty. A recovery without a cause identified is a recovery scheduled to repeat, and the causes are usually mundane; why is my pool green covers the common ones.
These are the readings we sign off on.
- Free chlorine at 3 to 5 ppm, and holding overnight within 1 ppm.
- Combined chloramines below 0.5.
- pH at 7.4 to 7.6.
- Alkalinity in range and stable across two visits.
- CYA at 30 to 50.
- Filter pressure back at its clean baseline, and written down.
- A main drain with a sharp edge to it when you look from the deck.
Our sign-off targets are deliberately tighter than the public health floor. The CDC’s home pool guidance sets a minimum of 1 ppm free chlorine, doubled to 2 ppm once there is CYA in the water, and a pH window running from 7.0 up to 7.8. Those are safe-to-swim numbers, not the numbers at which a pool that was green on Monday stays blue through a Texas week, so a recovery handed back at the bottom of that window has no margin.
How long a green pool recovery takes
A green pool recovery takes from two days to more than ten, depending on how green the pool starts. The ranges below are what we see, including the jobs that go long. Anybody promising a one day green-to-clean on a pool you cannot see the second step in is describing a chemical result, not a clear pool.
| Starting condition | Time to clear | Visits |
|---|---|---|
| Light green, floor still visible | 2 to 3 days | 1 to 2 |
| Solid green, steps not visible | 4 to 6 days | 2 to 3 |
| Dark green or black, surface film | 7 to 10 days | 3 to 4 |
| Swamp, standing debris, unknown equipment state | 10 days or more, sometimes with a drain | 4 or more |
| Mustard or black algae present | Add several days regardless of color | Extra visits, extra brushing |
What to demand from whoever does it
A green pool recovery should come with a paper trail, whether we do it or somebody else does, because the job is invisible once the water is blue.
- Readings from day zero, written down, including CYA.
- A dose that was calculated rather than estimated, and a willingness to say what it was calculated from.
- Photographs from the same position at each visit.
- The overnight loss test result, or an explanation of what was used instead.
- A filter clean included in the price, not billed as a surprise at the end.
- Final readings at sign-off, and a stated cause.
That is the standard we publish for our own green to clean recoveries, and it is the same documentation habit behind our photo reports on ordinary weekly visits. A company unwilling to hand over the numbers is asking to be trusted on a job that is designed to be checkable.
The chemistry is one day. Everything after that is circulation, filtration, and patience, and that is what you are paying for on a green to clean. If you are weighing quotes, green pool cleanup cost in DFW explains what moves the price.
