Swimart Bli Bli

Pool gone green?

Green water is algae, and algae means the chlorine ran out. Most green pools clear in two to five days with the steps in this guide.

Don't drain it. Treat it.

How green is it?

Look at the deepest part of the pool. How much of the floor you can see tells you how hard to hit it.

Light green or teal

Cloudy, but you can still see the floor.

Shock to
about 10 ppm
Clears in
1–2 days

Mid green

You can just make out the floor or the bottom step.

Shock to
about 20 ppm
Clears in
2–4 days

Dark green

You can't see the floor at all.

Shock to
about 30 ppm
Clears in
4–7 days

Working out your dose: 1 litre of 12.5% liquid chlorine adds roughly 12 ppm to every 10,000 litres of water. A 40,000 L pool needs about 3.5 L to reach 10 ppm. Not sure of your volume? Bring a water sample and we'll calculate it for you.

Before you start

  • Keep everyone out of the pool until it's clear and chlorine is back to normal.
  • Wear gloves and eye protection when handling chlorine and acid.
  • Never mix chemicals together, and add each one to the pool separately.
  • Always add chemicals to water, never water to chemicals.
  • Store chemicals in their original containers, out of reach of children.

Clearing a green pool

  1. Clear out the debris

    Scoop out leaves and sludge, then empty the skimmer and pump baskets. Anything left in the pool keeps feeding the algae and uses up chlorine.

  2. Test the water

    Bring a sample to Swimart Bli Bli, or test at home for chlorine, pH and stabiliser. Fill a clean bottle from elbow depth, away from the return jets.

  3. Bring the pH down to 7.2–7.4

    Chlorine works much harder at a lower pH. Add acid in small doses with the pump running and retest after an hour.

  4. Brush every surface

    Brush the walls, floor, steps and corners hard. This breaks up the algae so the chlorine can reach it.

  5. Shock the pool at dusk

    Pour the liquid chlorine slowly around the edge of the pool with the pump running. Adding it in the evening stops the sun burning it off before it works.

    Use the shock level from the severity scale for your shade of green.

  6. Run the pump around the clock

    Keep the pump on 24 hours a day until the water is clear. If you have a chlorinator, turn its output up to maximum.

  7. Clean the filter every day

    Dead algae clogs the filter fast. Hose out a cartridge or backwash a sand or glass filter whenever the pressure gauge climbs.

  8. Check the chlorine next morning

    If chlorine has dropped to zero overnight, the algae is still winning. Brush again and repeat the shock. Keep going until some chlorine is still there in the morning.

  9. Clear the cloudiness

    Once the water turns grey-blue and cloudy, the algae is dead. Add Aqua Health Liquid Floc and Clarifier at the dose on the label, then vacuum the settled dirt off the floor and clean the filter.

    Aqua Health Liquid Floc and Clarifier bottle

  10. Rebalance and go back to normal

    When the water is clear and chlorine holds overnight, rebalance the water, return to your normal pump run time and bring a final sample in to check.

What recovery looks like

The colour changes in stages. Cloudy grey water on day two means it's working.

Day 1

Green. Shock, brush and run the pump.

Day 2

Cloudy grey-blue. The algae is dead. Keep filtering.

Day 3

Hazy blue. Add Liquid Floc and Clarifier, vacuum, clean the filter.

Day 4 and on

Clear. Rebalance and test before swimming.

Yellow patches that keep coming back?

That's likely mustard algae. It shows as a yellow-green or dusty yellow film on walls, steps and shaded spots, and it returns within days of brushing. Chlorine alone won't clear it, so the steps above won't be enough on their own.

Close-up of yellow-green mustard algae coating a pool wall and floor
Yellow-green film along the wall and floor
Plunge pool with cloudy green water and a yellow tint on the walls and steps
Yellow tint on the walls and steps of a plunge pool
Aqua Health Pool Algaecide bottle

Treat it with Aqua Health Pool Algaecide

  1. Brush the yellow areas hard to lift the algae off the surface.
  2. Bring the pH down to 7.2–7.4.
  3. Add Aqua Health Pool Algaecide at the dose on the label for your pool volume, pouring it over the affected areas with the pump running.
  4. Keep the pump running and brush again each day while it works.
  5. Wash anything that's been in the pool, including toys, brushes, the pool cleaner and swimwear. Mustard algae hitches a ride and reinfects the pool.
  6. Clean the filter cartridge thoroughly once the patches are gone.

Read the safety directions on the bottle before use. Not sure it's mustard algae? Bring in a photo and a water sample.

OK to swim again when

  • You can clearly see the floor at the deep end.
  • Free chlorine is back to 1–3 ppm.
  • pH is between 7.2 and 7.6.

Call us if

  • You still can't see the floor after three days.
  • Chlorine keeps disappearing overnight after two shocks.
  • You see black spots, or yellow patches return after treating for mustard algae.
  • The pump, filter or chlorinator isn't working.

Stop it happening again

  • Test after rain and heatwavesSunshine Coast storms and hot spells burn through chlorine in a day or two.
  • Run the pump long enoughSix to eight hours a day in summer. Your chlorinator only makes chlorine while the pump runs.
  • Keep the filter cleanClean it when the gauge rises, and after any big storm.
  • Keep stabiliser at 30–50 ppmIt shields chlorine from the sun. We'll check it in your water test.
  • Check your chlorinator weeklyLook for a low salt warning and white scale on the cell.
  • Bring in a sample monthlySmall corrections are cheaper than a green pool recovery.