Cheat Sheet: Diagnosing a Green Pool

As Don Burke once said, “The hardest thing to keep right in any garden is water.” The same goes for your pool. Water naturally wants to go green, and as a pool owner, you’re constantly working against this. But don’t worry—while algae can be stubborn, it’s not invincible

A green pool means chlorine levels are too low, water circulation is poor, or pool chemistry is out of balance. This can happen due to hot weather, heavy rain, high bather loads, or equipment issues—all of which weaken your pool’s defenses. When chlorine can’t keep up, algae move in fast, turning the water cloudy and green.

The good news? A green pool is completely fixable. Follow this guide to diagnose the problem and get your pool back to crystal-clear perfection.

Step 1: Check Circulation and Filtration

If chlorine is the muscle behind keeping your pool clean, circulation and filtration are the bloodstream that keep everything moving. Without proper water flow, chlorine and other sanitizers can’t reach every corner of the pool, allowing algae to settle and grow.

Your pump ensures water moves through the system, distributing chemicals evenly, while the filter removes debris and contaminants that feed algae. If either isn’t working properly, chlorine becomes less effective, and the pool starts turning green.

Simple issues—like closed valves, a clogged pump basket, or a dirty filter—can restrict circulation, making it harder for your pool to stay clean. Running your pump for at least 8-12 hours a day, keeping the filter maintained, and ensuring return jets are angled for optimal flow can prevent stagnation and keep your water crystal clear.

If your pool is looking dull or cloudy, start here—sometimes, all it takes is a little flow to fix the problem!

Things to Check:

  • Are the valves open?
  • Is there power to the system?
  • Has the system accidentally been turned off?
  • Is there debris in the pump basket?
  • Is the filter pressure higher than normal?

What to do:

  • Open all necessary valves to ensure proper flow.
  • Clean the pump basket and/or filter to remove any clogs.
  • Check the fuse box for tripped breakers or power issues.
  • Run the pump for at least 8-12 hours a day to keep water circulating.

Step 2: Check Pool Balance

Pool chemistry isn’t just about dumping in chlorine and hoping for the best—it’s a delicate balance of different factors that all work together to keep your water clear and safe. When one element is off, it can throw everything out of whack, making it harder for chlorine to do its job. If chlorine levels are low, pH is too high or too low, or stabilizer levels are off, your pool becomes a perfect breeding ground for algae.

Think of it like baking a cake—each ingredient plays a specific role. Chlorine is the main ingredient that kills bacteria and algae, but pH levels determine how effective that chlorine actually is. If the pH is too high, chlorine becomes sluggish and weak. If it’s too low, the water becomes too acidic, which can damage equipment and irritate swimmers’ eyes and skin. Alkalinity acts as a buffer to keep pH stable, while stabilizer (cyanuric acid) protects chlorine from breaking down too quickly under the harsh Aussie sun.

When pool chemistry is properly balanced, chlorine works at full strength, water stays clear, and maintenance becomes much easier. A weekly test can save you from bigger headaches down the track!

Things to Check:

  • Salt: 1,000-2,000 ppm
  • Chlorine: 1-2 ppm
  • Free Chlorine: 0.5-1 ppm
  • pH: 7.4-7.8
  • Total Alkalinity: 100-150 ppm
  • Calcium Hardness: 200-300 ppm
  • Stabiliser (Cyanuric Acid): 30-50 ppm
  • Copper: 0.0 ppm

What to do:

  • Test your pool water weekly to stay on top of changes.
  • Take a sample to your local pool shop for a detailed analysis.
  • Regularly remove leaves, dirt, and other debris from the pool, pump, and filter.

Step 3: Check the Salt Chlorinator

Your salt chlorinator is the engine of your pool’s sanitation system—without it, your pool won’t get the chlorine it needs to stay clear. Instead of adding chlorine manually, the chlorinator converts salt or magnesium into chlorine through a process called electrolysis. When working properly, it provides a steady stream of sanitiser, keeping your pool water healthy with minimal effort. But if something goes wrong? Algae can take hold fast.

Several issues can cause a chlorinator to underperform. Sometimes, the settings aren’t high enough, especially during summer when chlorine demand increases. A high bather load or excess organic debris (like leaves, dirt, and sunscreen) can also eat up chlorine faster than the system can produce it. A clogged or calcified salt cell is another common culprit, as calcium buildup can block the plates and reduce chlorine output. If your chlorinator isn’t doing its job, you might find yourself constantly shocking the pool just to keep algae at bay.

Regular inspections and maintenance keep your chlorinator running at peak efficiency. By checking the salt cell for buildup, monitoring salt levels, and ensuring the system is set correctly, you can prevent chlorine shortages before they turn into a full-blown green pool disaster. A little maintenance now saves a lot of frustration later!

Things to Check:

  • Are salt levels between 1,000-2,000 ppm?
  • Is there calcium buildup on the salt cell (Green Cylinder)?
  • Is the salt cell clogged or dirty?
  • Are there error messages on the chlorinator’s control panel?
  • Is the chlorinator set to the correct output percentage?
  • Are the probes (Smart System) reading correctly?

What to do:

  • Superchlorinate (shock) the pool with liquid chlorine or granular shock.
  • Run the chlorinator at 100% output for 24 hours to boost chlorine levels.
  • If levels don’t improve, recheck your other water chemistry readings and adjust as needed.

Step 4: The Extra Mile – Cleaning & Algae Removal

Even with perfect chemistry and a working chlorinator, a dirty pool can still turn green. Leaves, dirt, and other organic debris don’t just make your pool look messy—they actually consume chlorine, leaving less available to fight algae and bacteria. If your pool is constantly struggling with algae, chances are it needs a deep clean.

Brushing the walls and floor helps break up algae colonies, making it easier for chlorine to kill them. Scooping removes dead algae and debris, preventing it from cycling back through the system. If the water is murky, a clarifier can help by clumping fine particles together so they get trapped in the filter better.

Sometimes, even after shocking, stubborn algae need an extra push—that’s where algaecides come in. Just be sure to choose one that’s compatible with your pool type. And don’t forget: keeping your basket and filter clean ensures your system can handle the job efficiently.

A little extra effort now means less maintenance later—and a pool that stays clear, inviting, and swim-ready!

Things to Check:

  • Is the pool full of leaves, dirt, or debris?
  • Has algae stuck to the walls or floor?
  • Is the water murky, even after shocking?

What to do:

  • Skim the pool to remove debris.
  • Brush the pool walls and floor to break up algae colonies.
  • If algae persists, use an algaecide suitable for your pool type.
  • If water is murky, use a clarifier, then clean the filter.
  • Keep the pump running for 24-48 hours after treatment.

Final Thoughts: Keep Your Pool Sparkling Year-Round

A green pool is frustrating, but with the right approach, it’s completely fixable. By checking circulation, balancing water chemistry, inspecting the salt chlorinator, and keeping your pool clean, you can restore your water to crystal-clear perfection.

The best way to avoid a green pool? Stay ahead of the problem. Test your water weekly, run your pump at least 8-12 hours a day, clean your filter, and inspect your salt cell regularly.

Still struggling? Take a water sample to your local pool shop or consult a pool technician. With the right care, your pool will be back to sparkling blue in no time—and stay that way all season long!

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