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Why Is My Pool Turning Green in Mordialloc and How Do I Fix It?

Author : Green Pool Cleaning | Published On : 23 Mar 2026

There's nothing quite like stepping out into your backyard on a warm Mordialloc summer day, ready to dive into your pool — only to find the water has turned an alarming shade of green. It's a frustrating sight, and one that many pool owners in the area know all too well. The good news? A green pool is a common problem, and with the right knowledge and action plan, it's entirely fixable.

In this guide, we'll walk you through exactly why your pool is turning green, what's happening beneath the surface, and the step-by-step process to restore it to sparkling, swim-ready condition. Whether you're tackling it yourself or considering a professional Green Pool Cleaning Mordialloc service, this guide has everything you need to make the right decision.

The Real Reason Your Pool Is Turning Green

Before you can fix the problem, you need to understand what's causing it. In almost every case, a green pool comes down to one culprit — algae.

Algae are microscopic plant-like organisms that thrive in water. They're naturally present in the environment and can enter your pool through rainwater, wind, contaminated pool equipment, or even swimwear. Under normal circumstances, a properly maintained pool's chemical balance keeps algae from growing. But when that balance is disrupted, algae can multiply rapidly — and within 24 to 48 hours, your once-clear pool can turn noticeably green.

What Triggers Algae Growth?

Several factors can create the perfect environment for algae to flourish, and for pool owners in Mordialloc, the local climate plays a significant role.

1. Low or Depleted Chlorine Levels Chlorine is your pool's primary defence against algae and bacteria. When chlorine levels drop too low — whether due to heavy pool usage, hot weather, or simply forgetting to add it — algae seize the opportunity to take hold. Mordialloc's warm summers can burn through chlorine faster than you might expect, making regular testing absolutely essential.

2. Poor Water Circulation A pool that isn't circulating properly creates stagnant pockets of water where algae can grow undisturbed. If your pump isn't running long enough each day, or if your filter is clogged or underperforming, poor circulation becomes a major contributing factor.

3. Imbalanced Pool Chemistry It's not just about chlorine. If your pool's pH, alkalinity, or cyanuric acid levels are off, even adequate amounts of chlorine won't work effectively. High pH levels, in particular, significantly reduce chlorine's sanitising ability, leaving your pool vulnerable.

4. Warm Weather and Sunlight Algae thrive in warm, sunlit conditions — and Mordialloc's summer weather provides exactly that. Ultraviolet rays from the sun also break down unstabilised chlorine quickly, accelerating the problem. Extended heatwaves, which are increasingly common in the region, can turn a slightly green pool into a swamp in a matter of days.

5. Lack of Regular Maintenance Skipping routine cleaning, brushing, and chemical checks allows algae to build up gradually. Many homeowners don't notice the early signs — a slight cloudiness or faint greenish tinge — until the problem becomes serious.

How to Tell How Bad the Problem Is

Not all green pools are the same. The severity of your algae problem will determine how much work is ahead of you.

  • Light green or slightly cloudy — Early-stage algae growth. Relatively easy to treat with shock treatment and chemical adjustment.
  • Bright or medium green — Moderate infestation. Will require a thorough shock treatment, brushing, and several days of filtration.
  • Dark green or murky — Severe algae bloom. You can barely see the bottom of the pool. This requires an intensive treatment plan and possibly professional intervention.
  • Black or dark patches on walls — Black algae, which is the most stubborn variety and deeply roots itself into pool surfaces. This is the hardest to treat and almost always benefits from professional help.

Step-by-Step: How to Fix a Green Pool in Mordialloc

Step 1: Test Your Water First

Before adding any chemicals, test your pool water thoroughly. You can use a home testing kit or take a water sample to your local pool supply store in Mordialloc for a professional analysis. You need to check:

  • Free chlorine levels
  • pH (ideal range: 7.2 – 7.6)
  • Total alkalinity (ideal range: 80 – 120 ppm)
  • Cyanuric acid (stabiliser) levels

Understanding where your water stands gives you a clear picture of what needs correcting.

Step 2: Balance the pH and Alkalinity

Before shocking your pool, bring your pH and alkalinity into the correct range. If the pH is too high, use a pH decreaser (sodium bisulphate). If alkalinity is off, use an alkalinity increaser or reducer accordingly. Skipping this step means your shock treatment won't work as effectively, wasting both time and money.

Step 3: Shock the Pool

Pool shocking involves adding a large dose of chlorine — typically three to five times the normal amount — to kill algae and bacteria rapidly. For a moderately green pool, a single shock treatment may be enough. For a severely green pool, you may need to repeat the process over two to three days.

Always shock your pool in the evening or at night. Sunlight degrades chlorine quickly, so treating at night gives the chemicals time to work without being diminished by UV rays.

Step 4: Brush the Pool Thoroughly

Don't skip this step. Brushing the walls, floor, and steps of your pool loosens algae from the surfaces and exposes them to the chlorine in the water. Use a stiff-bristled pool brush and work methodically across every surface. For black algae, you'll need to brush aggressively and repeatedly over several days.

Step 5: Run Your Filter Continuously

After shocking and brushing, run your filter continuously — 24 hours a day if possible — until the water clears. The filter's job is to capture the dead algae particles and remove them from the water. Clean or backwash your filter regularly during this period, as it will become clogged quickly.

Step 6: Add an Algaecide

Once the chlorine levels begin to normalise, adding an algaecide helps kill off any remaining algae and prevents a recurrence. Choose a quality pool algaecide and follow the dosage instructions carefully.

Step 7: Vacuum the Pool

As the water clears, you'll likely notice dead algae settling on the pool floor. Vacuum this debris out, vacuuming to waste if possible so the dirty water bypasses your filter and goes directly out of the pool system.

Step 8: Retest and Adjust

Once your pool looks clear, test the water again. Fine-tune your chemical levels and make sure everything is within the ideal range before declaring the job done.

Preventing Your Pool from Going Green Again

Fixing a green pool is one thing — keeping it clear is another. Here's how to stay ahead of the problem:

  • Test your water at least twice a week during summer months in Mordialloc.
  • Run your pool pump for a minimum of 8 hours per day in hot weather.
  • Brush your pool walls and floor weekly to prevent algae from taking hold.
  • Clean your filter regularly and replace it when it's past its useful life.
  • Shock your pool after heavy rain, pool parties, or periods of intense heat.
  • Use a pool stabiliser (cyanuric acid) to protect chlorine from being destroyed by sunlight.

When to Call a Professional Green Pool Cleaning Service in Mordialloc

Sometimes, a green pool is beyond a simple DIY fix — particularly if the algae growth is severe, you're dealing with persistent black algae, or the pool chemistry has been neglected for a long time. In these cases, calling a professional green pool cleaning service in Mordialloc is the smartest and most cost-effective decision. Professionals have the industrial-grade equipment, expertise, and chemicals to restore even the most stubborn green pool efficiently and safely.

Final Thoughts

A green pool in Mordialloc is never something to ignore. What starts as a minor algae issue can quickly become a full-blown health hazard if left untreated. The good news is that with prompt action, the right chemicals, and consistent maintenance habits, you can enjoy a clean, clear, and safe swimming pool all season long. And when the problem feels too big to handle alone, the local experts are always just a phone call away.