Green Pool? Here's How to Fix It Fast

Why Does a Pool Turn Green?

A green pool is an algae bloom. Algae establishes when chlorine levels drop too low to sanitise the water — usually caused by a combination of heat, sunlight, heavy use, and missed maintenance. In Perth's summer, a pool can go from clear to green in as little as 48 hours if the chlorine is exhausted and conditions are right.

The good news: a green pool is fixable. The process takes between 24 hours and 4 days depending on how severe the bloom is.

Step 1: Test Your Water First

Before adding any chemicals, test your pH, chlorine, alkalinity, and stabiliser levels. Adding shock chlorine to a pool with a pH above 7.8 is largely ineffective — the chlorine won't work properly. Balance your pH to between 7.2 and 7.4 first, then proceed.

Step 2: Shock the Pool

Shock treatment means adding a large dose of chlorine to overwhelm and kill the algae. For a light green pool, you'll typically need 2-3 times the normal chlorine dose. For a dark green or black pool, you may need significantly more — sometimes 5-10 times normal levels.

Use granular calcium hypochlorite or liquid chlorine. Add it in the evening to prevent UV degradation. Run your pump continuously during treatment.

Warning: Never mix pool chemicals. Always add chemicals to water, never water to chemicals. Allow each chemical to circulate fully before adding another.

Step 3: Run Your Pump Continuously

Don't turn your pump off during treatment. Continuous circulation is essential to distribute the chemicals and filter out dead algae. You may need to clean your filter multiple times during the process as it fills with dead algae matter.

Step 4: Brush the Pool

Brush every surface — walls, floor, and steps — to dislodge algae that's attached to the pool surface. Do this before shocking and again 12 hours after. The physical agitation helps the chlorine reach and kill embedded algae.

Step 5: Vacuum and Backwash

Once the algae has died (the water will turn from green to a cloudy grey-white), vacuum the pool to waste — not through your filter, directly to waste — to remove the dead algae. Then backwash your filter thoroughly. Repeat until the water clears.

Step 6: Balance and Test Again

Once clear, test and balance all chemical levels again. The shock treatment will have consumed your stabiliser and may have affected other parameters. Get everything back into range before swimming.

How to Prevent It Happening Again

•       Maintain chlorine levels between 1-3 ppm at all times

•       Check levels weekly with a home test kit — don't guess

•       Run your pump for at least 6-8 hours per day in summer

•       Keep your stabiliser (cyanuric acid) between 30-50 ppm to protect chlorine from UV

•       Book a monthly professional service to catch problems before they escalate

When to Call a Professional

If the pool hasn't cleared after 72 hours of treatment, or if you're unsure about chemical dosing, call a professional. Overdosing chemicals is costly and can damage pool surfaces. A professional service for a severe green pool is almost always more cost-effective than multiple rounds of DIY treatment that miss the mark.

Need help with your pool or home maintenance? Call Macca's on 0492 313 347 or visit maccaspoolandhousemaintenance.com.au for a free quote. Servicing Duncraig, Joondalup, Hillarys, Karrinyup, Sorrento, Scarborough and surrounding suburbs.