How to Fix a Green Pool Fast — Sydney Pool Owner's Guide
Share
You walk outside, look at your pool and — yep, it's green. Whether it happened overnight after heavy rain or crept up on you over a few warm days, a green pool is one of those things that needs to be dealt with quickly before it gets worse.
The good news? You don't need to drain the pool or call a professional. With the right products and a bit of patience, most green pools can be cleared up within 3 to 5 days. Here's exactly how to do it.
In this guide
Why Does a Pool Turn Green?
Almost always, a green pool comes down to one thing — algae. Algae are microscopic organisms that thrive in warm, poorly sanitised water. When your chlorine levels drop too low — even briefly — algae can bloom rapidly, turning your pool green within 24 to 48 hours.
Common triggers include:
- Heavy rain — dilutes your pool chemicals and throws off the pH balance
- Hot weather — warm water accelerates algae growth
- Not enough chlorine — the most common cause by far
- Poor circulation — dead spots in the pool where water doesn't move allow algae to settle
- Forgetting to run the filter — your filter is your first line of defence
How Bad is Your Green Pool?
Before you start, it helps to know what you're dealing with. The severity of the problem affects how much product you'll need and how long it'll take to clear.
- Light green / teal: Algae is just starting to bloom. You can see the bottom of the pool clearly. This is the easiest to fix — usually 1 to 2 days
- Medium green: The water is murky and the bottom is hard to see. A few days of treatment needed
- Dark green / black-green: Heavy algae bloom, you can't see the bottom at all. This will take 3 to 5 days and more product
What You'll Need
Here's what we recommend at Drive In Pool & Spa — this is the combination we advise customers to use for the best results:
- Liquid chlorine (drum) — a 10 or 15 litre drum of liquid chlorine is our go-to recommendation for clearing a green pool. It works faster than granular shock and is easier to distribute evenly around the pool
- Hydrochloric acid (2.5 litres) — used to bring your pH down before treating. High pH reduces how effective chlorine is, so getting this right first makes a big difference
- Algaecide — kills the algae and prevents it from coming back once the chlorine has done its job
- Clarifier — helps clump together the dead algae particles so your filter can remove them more effectively, clearing the water faster
- Pool brush — essential for breaking up algae on walls, floor and steps before adding chemicals
- Water testing kit or test strips — to check your pH, chlorine and alkalinity before and after treatment
- Pool filter — needs to run continuously during treatment
- Manual or automatic vacuum — to clean up dead algae from the bottom once the water starts clearing
You can find liquid chlorine, algaecide, clarifier and acid in our online store or pick them up in store at Gordon — we'll help you choose the right quantities for your pool size.
Step-by-Step: How to Fix a Green Pool
Test Your Water First
Before adding any chemicals, test your water. You need to know your current pH, chlorine and alkalinity levels. Aim for:
- pH: 7.2 – 7.6
- Alkalinity: 80 – 120 ppm
- Chlorine: Currently low — that's why you're here
If your pH is way off, adjust it first — chlorine shock is far less effective in high pH water.
Brush the Pool Thoroughly
Grab your pool brush and scrub every surface — walls, floor, steps and corners. This breaks up the algae colonies and exposes them to the chemicals you're about to add. Don't skip this step — it makes a significant difference to how fast the pool clears.
Lower the pH with Acid
Before adding chlorine, lower your pH using hydrochloric acid. We recommend having 2.5 litres on hand. Aim to bring your pH down to around 7.2 — chlorine is significantly more effective at lower pH levels, so this step makes everything that follows work harder.
- Add acid slowly around the perimeter of the pool with the pump running
- Never add acid and chlorine at the same time — wait at least 30 minutes between the two
- Re-test after adding and adjust further if needed
Hit it with Liquid Chlorine
This is the main event. We recommend using liquid chlorine (drum) rather than granular shock — it distributes more evenly, works faster and is easier to handle for a green pool treatment.
- For a light green pool: one standard dose as per the label
- For medium to dark green: double or triple dose depending on severity
- Add liquid chlorine in the evening or at night — UV from sunlight breaks it down quickly
- Walk slowly around the pool pouring it in evenly — never dump it all in one spot
Add Algaecide
Once the chlorine has been in the pool for at least 30 minutes, add your algaecide as per the product instructions. Algaecide works alongside the chlorine to kill remaining algae and prevent new growth from taking hold. Walk slowly around the pool adding it evenly to the water.
Run the Filter Continuously
Your filter needs to run 24 hours a day until the pool is clear. The filter is what physically removes the dead algae from the water. Clean or backwash the filter every 12 to 24 hours during treatment — a clogged filter will slow everything down significantly.
Brush Again the Next Day
After the first treatment, brush again the next morning. You'll see dead algae on the walls and floor — brush it into the water so the filter can pick it up. Repeat daily until the pool is clear.
Vacuum the Dead Algae
Once the water starts clearing — usually after day 2 or 3 — vacuum the dead algae from the bottom of the pool. Use a manual vacuum or an automatic suction-side vacuum cleaner for this job.
A manual vacuum connected to your skimmer or a suction-side automatic vacuum are both fine to use — the debris gets sent straight to your filter rather than through the robot's internal system.
Add Clarifier & Re-test
Once the water is starting to clear, add your clarifier as per the product instructions. Clarifier works by binding together the tiny dead algae particles that are too small for your filter to catch on its own — clumping them into larger particles that the filter can remove. This significantly speeds up how fast the water clears.
Then test the water again and balance your chemicals. After heavy chlorine treatment, your chlorine level will be very high — wait until it drops back to 1–3 ppm before swimming. Check your pH is back in the 7.2–7.6 range and adjust alkalinity if needed.
Need pool chemicals in Gordon NSW?
We stock chlorine shock, algaecide and a full range of pool chemicals in store at Gordon — open 7 days. Not sure which products are right for your pool? Give us a call and we'll help you out.
Shop Pool Chemicals → Call 02 9499 9646How Long Does it Take to Clear a Green Pool?
It depends on how green the pool was to start with:
- Light green: 1 – 2 days
- Medium green: 2 – 3 days
- Dark green: 3 – 5 days
The most important factors are running the filter continuously, brushing daily and cleaning the filter regularly. Skimping on any of these will slow things down.
How to Prevent a Green Pool From Happening Again
Once you've put in the effort to clear a green pool, the last thing you want is for it to happen again. Here's how to keep it clear:
- Test your water weekly — catch chemical imbalances early before algae takes hold
- Maintain chlorine levels at 1–3 ppm consistently
- Run your filter at least 8 hours a day — more in summer
- Brush the pool weekly even when it looks clean
- Shock after heavy rain — rain dilutes your chemicals every time
- Use a robotic pool cleaner regularly — keeping the pool physically clean reduces the conditions algae needs to grow. Just remember — never run it in a green pool, always wait until the water is clear first
- Add algaecide as a preventative at the start of summer or after heavy rain
Final Thoughts
A green pool looks terrible but it's not the end of the world. With chlorine shock, algaecide, a good brush and a running filter, you can have a clear, sparkling pool again within a few days. The key is acting quickly and being consistent with your treatment.
If you're in the Gordon, North Shore or Northern Suburbs area and need advice or products, come in and see us at Drive In Pool & Spa Warehouse. We're open 7 days and happy to help you get your pool back in shape.
Shop our full range of pool chemicals online — we ship Australia-wide.