Sydney winters can be relentless. A few weeks of steady rain, grey skies, and cooler temperatures, and your pool can turn on you fast. Right now, pools across the Eastern Suburbs, Northern Beaches, and North Shore are under pressure, and many owners won’t realise there’s a problem until the water starts looking murky or green.
Rain doesn’t just fill your pool. It dilutes your chemicals, drops your pH, washes in debris, dirt, and contaminants from surrounding surfaces, and throws off the balance you’ve worked to maintain. Left unchecked, that’s the perfect setup for an algae bloom.
Here’s what to do.
Step 1: Check Your Water Level
Heavy rain raises your water level, often above the skimmer box. When that happens, your skimmer stops working properly and surface debris stays in the pool instead of getting pulled out. If your water level is too high, use a submersible pump or your waste setting on the filter to bring it back to the midpoint of the skimmer opening.
Don’t skip this step. Everything else relies on your filtration working correctly.
Step 2: Run Your Filter Longer Than Usual
After rain, run your filter for longer than your normal cycle. If you’re usually running six to eight hours, bump that up to ten or twelve hours for the next few days. The goal is to push as much water through the filter as possible to clear out the fine particles and contaminants that rain brings in.
If your filter is due for a clean or backwash, do it now. A clogged or dirty filter will slow your recovery down significantly.
Step 3: Test Your Water Chemistry
This is the most important step, and the one most people get wrong by guessing.
Rain is slightly acidic, and when a large volume enters your pool it drags your pH down and dilutes your sanitiser levels. That combination, low pH and low chlorine, is exactly what algae needs to take hold.
Test for:
- pH (target 7.2 to 7.6)
- Total alkalinity (target 80 to 120 ppm)
- Chlorine (free chlorine target 1 to 3 ppm)
- Stabiliser (cyanuric acid) target 30 to 50 ppm
Bring your total alkalinity up first if it’s low, then adjust pH. Once those are stable, your chlorine will work far more effectively.
Step 4: Shock Your Pool
Even if your water still looks clear, shock it. After significant rain, your chlorine demand increases because the water is full of organic material, leaves, pollen, soil run-off, and diluted sanitiser. A shock dose of chlorine burns through that load and resets your sanitiser levels.
Use a quality granular chlorine shock and follow the dosing on the label for your pool volume. Run your pump while you add it and keep it running for several hours after.
Step 5: Brush the Walls and Vacuum
Rain stirs up debris and deposits it on your pool walls, floor, and in the corners. Algae will start on surfaces before it becomes visible in the water. Brush every surface thoroughly, paying attention to steps, corners, and behind ladders. Then vacuum to waste if you can, so you’re removing the debris rather than pushing it back through your filter.
If you can see early signs of green or cloudy water, do this before and after shocking.
A Word on Sydney’s Winter Weather Patterns
Sydney winters can swing between weeks of heavy rain and sudden dry spells that follow just as quickly. When the rain stops and temperatures drop, pool owners often switch off. The pool looks fine. Nothing seems urgent. But that’s when things can go sideways.
Cooler temperatures slow algae growth, but they don’t stop it. And if your chemistry has been off for a week or two during wet weather, you may already have a problem building beneath the surface. Consistent maintenance through winter, not just reactive fixes after storms, is what keeps a pool genuinely healthy year-round.
When It’s Worth Getting Help
These five steps will give most pools a solid foundation after rain. But if your water has already turned green, if it’s stayed cloudy after balancing, or if you’re not confident in your test readings, it’s worth calling in a professional.
The Pool Service Co. services pools across Sydney’s Eastern Suburbs, Northern Beaches, Mosman, North Sydney, and the wider North Shore. One of the real advantages of ongoing pool management is that your dedicated Pool Tech already knows your pool. They know how it responds to rain, how it behaves in winter, and where it tends to lose balance. When a weather event hits, that knowledge means faster diagnosis and a faster fix.
If you want the peace of mind of knowing your pool is in good hands this winter, book a free pool assessment or call and speak with a Pool Tech directly.
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