Green pool recovery in Australia: from algae to crystal clear in 5 days

Australian pools go green in two classic ways: the after-storm bloom, when a January downpour dumps debris into warm water and drowns your chlorine, and the winter slide, when a pool ignored through June, July and August greets you in spring looking like a farm dam. The fix is the same for both. No algaecide shortcut, no magic powder — just chlorine, brushing, and pump runtime.

Day 0: assess and balance

Before you spend a dollar on chemicals, test the water. The two numbers that decide your fight are stabiliser (cyanuric acid, or CYA) and pH.

Under Australian sun most outdoor pools carry 30–50 ppm of stabiliser, and it creeps upward every time you add stabilised chlorine. If CYA reads over 60 ppm, drain a third of the pool and refill before you start — and check your water utility's rules on draining pool water first, especially where restrictions apply. You cannot win against algae if chlorine cannot reach its shock level.

If pH is over 7.6, bring it down to 7.2 with pool acid (hydrochloric acid) from any pool shop or hardware store. Chlorine kills far faster at slightly acidic pH.

Clean the filter completely — hose out the cartridge or backwash the sand. A dirty filter will choke on dead algae within 12 hours.

Found the green in July? Fix it now. Algae grows slowly in cold water, so a winter recovery is cheaper and faster than facing a full swamp in November.

Day 1: SLAM (shock level and maintain)

SLAM means raising free chlorine (FC) to ten times your CYA level and keeping it there. So 30 ppm CYA = 30 ppm free chlorine target.

Doses assume 12.5% liquid pool chlorine, the standard strength at Australian pool shops — check the drum and scale for your own pool's volume.

Timing matters more here than almost anywhere: Australian UV tears through chlorine in the middle of the day. Dose after sunset, brush every wall and the floor, and run the pump 24 hours a day until this is over.

Day 2: retest and recharge

Test free chlorine in the morning. It will have dropped a lot — that is the algae dying. Bring FC back up to the shock target, brush again, and keep the pump running.

The water will turn from green to grey. Grey is dead algae. You are winning.

Days 3 to 4: clean the filter, keep brushing

Backwash or rinse the filter every 12 to 24 hours — it is doing the heaviest work of its life. The water will go cloudy and milky before it clears. Hold chlorine at shock level. Keep brushing.

Day 5: the overnight chlorine loss test

Under harsh sun, this is the only honest test. At sunset, record free chlorine. Before sunrise, test again. If you lost less than 1 ppm overnight and the water is clear, the algae is dead. Let chlorine drift down to 1–3 ppm — the sun will handle that quickly — and resume normal care.

If you lost more than 1 ppm, hold shock level another day and retest.

What about algaecide

Polyquat 60 algaecide is a useful preventive at the start of the season. It is not a fix for an active green pool — tipped into a swamp it mostly wastes money and can cause foaming. Save it for after recovery.

When to call a pro

If the pool will not respond after five days of correct SLAM, you may have mustard algae — common in the warmer parts of Australia — black algae, or phosphates feeding new growth as fast as you kill it. A pool technician can identify and treat it; get a couple of quotes, because a full recovery usually means several visits.

Green pool FAQs

Will algaecide alone clear a green pool? No. Algaecide is a preventive. Once a pool is green, you need chlorine at shock level for several days.

How much chlorine will I need? For a 50,000 litre pool with moderate algae, plan on 30 to 60 litres of liquid chlorine across the five days. Price it at your local pool shop before you start — 15 litre drums are far cheaper per litre than small bottles.

Can I swim before it is fully clear? No. Cloudy water hides the bottom, which is a drowning hazard, and shock-level chlorine is rough on skin and togs. Wait for full clarity and FC below 5 ppm.

Do I need to drain the pool? Only if CYA is over 60 ppm, or the pool is such a swamp that chlorine would cost more than a refill. Most green pools recover without draining — and check your water utility's rules if you do.

Why does my pool go green after every summer storm? Rain dilutes your chlorine, washes in debris and phosphates, and warm December-to-February water does the rest. Test and re-dose the same day a storm passes, not next weekend.

My salt pool went green — how? A salt chlorinator makes chlorine slowly, and a bloom can outrun it. Run the SLAM with liquid chlorine, then check the cell for scale and turn the output up for the rest of summer.

A clear pool earns its keep in an Australian summer

With a season that runs from before Christmas well into autumn — and nearly year-round in the north — a clear backyard pool is a genuine asset, and hourly pool hire is the way to make it pay. Pool Rental Near Me lets you list your pool free, and founding hosts pay 0% host fees, forever — you keep 100% of your price. Prices on the site currently display in US dollars, and hosts are paid out in Australian dollars via Stripe. For context from the more mature US market: top backyard pools in Southern California earn $800–$1,000 in a good summer week. That is US data, not an Australian promise, but it shows what hot-week demand looks like.

Start with our guide to renting out your pool in Australia, see how hourly hire works in Sydney, and once your water passes the overnight test, List your pool.