Pool cloudy after rain? How to clear it in a Queensland storm season
Get the leaves and dirt out, clean the filter, test pH and chlorine, then shock dose with the pump running. Take the robot out before any chemicals go in.
Cloudy after rain usually means two things at once: dirt and debris washed in, and chlorine used up fighting it. Get the debris out, clean the filter, set pH, then shock dose with the pump running. Take the robot cleaner out before any chemicals go in, and don't swim until the water's clear and back in range.
The steps and numbers below come from SA Health, NSW Health and Queensland Health, plus the makers' robot manuals. They're all linked at the bottom.
It's rarely the rain itself
Rain doesn't add as much water as people think. Say 50 mm falls on a 7 m by 3.5 m pool. That's 24.5 m² × 0.05 m, about 1,200 litres, into a pool that holds around 33,000. A few per cent. It thins your chlorine and salt a bit, but it doesn't turn water milky on its own.
What does is everything that comes in with it. Soil off the garden beds, leaves and bark, dust, and runoff from paths. SA Health says algae get into pools on rain, wind and soil, and it recommends a shock dose after a rainstorm.
Read the water first
How it looks tells you where to start.
| What you see | Likely cause | First move |
|---|---|---|
| Dull haze, floor visible | Chlorine used up | Filter clean, then shock |
| Milky, can't see the floor | Fine soil in suspension | Shock, then floc if no change |
| Green tinge or slimy walls | Algae | Brush, then shock |
| Brown water, silt on floor | Floodwater got in | Call the pool shop |
Clear it in five steps
- Get the debris out before it sinks and breaks down. Scoop the surface, empty the skimmer box and pump basket, and brush the walls and steps so stuck-on muck goes into suspension where the filter can get it.
- Take the robot out and leave it out until step 5 is done. More on why below.
- Clean the filter. SA Health says that if the filter isn't working properly, the chemicals you add won't be effective. Backwash a sand or glass filter, or hose a cartridge, following the maker's directions.
- Test and fix pH. SA Health says chlorine works properly between 7.2 and 7.6. Check total alkalinity too, because SA Health lists it as one of the things that prevents cloudy water. It recommends 60 to 200 mg/L.
- Shock dose. SA Health's method is to raise free chlorine to 10 mg/L, hold it there for at least an hour, and run the pump and filter the whole time.
Then leave the pump on. SA Health says a filter should be able to turn over the whole pool in six to eight hours, and NSW Health suggests running it 8 to 12 hours a day. After a storm, run it longer than usual until the water clears.
A worked dose for 33,000 litres
Take a 7 m by 3.5 m pool, 1.0 m at the shallow end and 1.7 m at the deep end. The average depth is 1.35 m, so it holds 7 × 3.5 × 1.35 = 33.1 m³. Call it 33,000 litres. Odd shape? Our pool volume calculator will work it out.
SA Health's example shock dose is 200 mL of liquid chlorine (12.5% available chlorine) per 1,000 litres, or 30 g of granular calcium hypochlorite per 1,000 litres. For this pool that's 33 × 200 mL, about 6.6 litres of liquid, or 33 × 30 g, about 990 g of granular.
That's an estimate. Strengths vary between products, so follow the label on yours and don't mix chemicals. Don't swim until free chlorine is back down to 4 mg/L. SA Health says that can mean leaving the pool overnight.
Why the robot sits it out
Zodiac's FreeRider FR350 iQ manual says not to leave the cleaner in the pool during any chemical treatment. Maytronics' Dolphin Liberty 200 and 400 manual lists water limits of chlorine 4 ppm max and pH 7.0 to 7.8, so a pool at 10 mg/L is well outside what it's built for. Check the limits in your own manual.
Once chlorine is back under 4 and the water's clear, put it back in for a floor and wall cycle. It'll pick up what settled on the floor, and rinsing its filter after each run keeps it from clogging. If yours starts sliding off the walls after a storm, it's often slimy walls rather than a fault. Our not-climbing checklist covers that. Under gum trees and fed up with scooping? Our guide to robots for leaves compares basket sizes and filters.
Still milky after a day
Fine soil can be too small for a pool filter to catch, so the water stays milky even with good chlorine. NSW Health's advice for dirty water after a storm or flood is to ask a pool shop about flocculating it. Floc clumps the fine particles so they sink, and NSW Health says to vacuum that material to waste, not through the filter. Then it says to bring free chlorine up to 5 mg/L and pH to 7.2, at least overnight with the filter running, using enough liquid chlorine to do that (check the label).
Keep the robot out for this one too. The Dolphin Liberty manual says not to use the robot if you've added liquid flocculant or any other clarifier, because they block and damage its filters. Floc settled on the floor is a job for a manual vacuum on the waste setting.
If you run a salt chlorinator, test the salt once the water's sorted. Rain and vacuuming to waste both drop it, and NSW Health says to adjust the salt concentration afterwards. Use the range in your chlorinator's manual.
If floodwater got into the pool, this page isn't the fix. Queensland Health says a normal pool filter shouldn't be relied on after a flood, and that a flood-affected in-ground pool needs emptying, but not while the ground around it is saturated. Talk to your pool shop and council first, and get a licensed electrician to check the pump and power before you switch anything on.
Before the next storm
Storms keep coming right through a Queensland summer, so it pays to get ahead of them. Keep chlorine at SA Health's 1 to 3 mg/L (ideally 2) so there's something in reserve when the debris comes in, and trim branches that hang over the water. If heavy rain overfills the pool, lower it using your filter's waste setting as the manual describes. Our Queensland summer pool checklist has the weekly routine, and the fence and gate checks to do after a big blow.
Sources (checked October 2026): SA Health: Pools at home and maintaining them · NSW Health: Cleaning swimming pools after floods or storms · NSW Health: Healthy swimming pools · Queensland Health: Swimming pool safety after a disaster · Zodiac FreeRider FR350 iQ owner's manual (ANZ) · Maytronics: Dolphin Liberty 200/400 user manual.
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Can I swim in a cloudy pool?
No. SA Health says not to use a home pool if the water is cloudy or dirty, or if chlorine or pH is out of range. Wait until it's clear and back in range.
Should I drain a pool after a flood?
Not straight away. Queensland Health says a flood-affected in-ground pool needs emptying, but not while the ground around it is still saturated, because that can cause structural damage. Talk to your pool shop and council first.