Pool Green After Rain Australia | Test, Balance and Clear It
Pool turned green after heavy rain? Follow the right Australian recovery order: remove debris, test pH and chlorine, calculate treatment, filter, brush, and retest.
Pool Green After Rain Australia: What to Do First
Heavy Australian rain can dilute sanitiser, move pH, wash leaves and soil into the water, and increase the load on your filter. If warm weather follows, algae can become visible quickly.
Do not start by throwing several chemicals into the pool. The fastest reliable recovery is clean → circulate → test → correct → filter → retest.
First: Is the Water Safe to Enter?
Keep swimmers out when the water is green, the floor is not clearly visible, or free chlorine and pH have not been verified. Never add chemicals while anyone is in the water.
If floodwater, sewage, or other contaminated runoff entered the pool, ordinary algae treatment is not enough. Follow your state health authority or a pool professional's contamination process.
The First 30 Minutes
1. Remove leaves and debris. Empty the skimmer and pump baskets. 2. Check the equipment. Confirm the pump is primed and water is moving through the filter. 3. Brush walls, steps, corners, and the floor. This exposes algae to sanitiser and filtration. 4. Test before dosing. Measure free chlorine, pH, and total alkalinity. Also test CYA in outdoor chlorine pools and salt in saltwater pools. 5. Record pool volume. If you are unsure, use the pool volume calculator before calculating chemicals.
Correct Chemistry in the Right Order
1. Stabilise alkalinity and pH
Rain can move water balance in either direction depending on the pool, fill water, debris, and chemicals already present. Test rather than assuming rain always lowers pH.
Australian health guidance commonly places pH around 7.2–7.8, while this site's normal calculator targets 7.2–7.6. Correct large alkalinity problems before fine-tuning pH.
- [Pool alkalinity calculator →](/guides/pool-alkalinity-calculator-australia)
- [How to lower high pH →](/blog/how-to-lower-pool-ph)
- [How to raise low pH →](/blog/how-to-raise-pool-ph)
2. Restore sanitiser
For chlorine and saltwater pools, calculate the increase from the measured free chlorine, pool litres, and the strength printed on the product. Do not use a generic scoop count.
Use the pool shock calculator by volume when the product label or water condition calls for a shock treatment. For an ordinary low reading, enter the results into the full pool calculator.
3. Check CYA in outdoor chlorine pools
Rain and overflow can dilute stabiliser. Too little CYA allows Australian UV to consume chlorine quickly; too much slows disinfection and normally requires dilution.
Use the Australian stabiliser calculator, but do not add CYA to indoor pools, spas, bromine pools, or Naked freshwater systems.
Filter and Brush Until Clear
- Run circulation continuously during the initial recovery if your equipment manufacturer permits it.
- Brush at least daily while algae remains visible.
- Backwash or clean the filter when pressure reaches the manufacturer's cleaning threshold.
- Vacuum settled material. Use waste mode where appropriate so dead algae does not immediately return through the system.
- Retest after the chemical label's mixing time and before adding more.
Green colour can also come from metals rather than algae. If the water is clear but tinted, or it changed colour immediately after adding chlorine, take a water sample to a pool shop before applying more algaecide or shock.
Saltwater and Freshwater Differences
Saltwater pool: Rain can dilute salt and free chlorine at the same time. Restore water balance first, then confirm the chlorinator's salt range and output.
Naked freshwater pool: Do not follow a traditional shock routine. Check the manufacturer's pH and copper ranges and use the dedicated Naked pool green-after-rain guide.
Prevent the Next Spring Bloom
- Test before forecast storms and again after overflow or a major top-up.
- Remove organic debris promptly.
- Keep the filter clean and circulation appropriate for water temperature.
- Maintain the correct CYA range in outdoor chlorine pools.
- Start the [Australian pool opening checklist](/blog/pool-opening-checklist) before sustained October–December heat.
Calculate the Recovery Dose
Enter the readings you measured—not estimates—to get a volume-based diagnosis.
Sources: HealthyWA pool and spa guidance and Better Health Channel pool water quality.