It was clear yesterday. Today it's green. It feels sudden, but a pool rarely turns green out of nowhere. Algae is almost always present in small amounts. It takes over when chlorine has been running low for a few days and conditions suit it: warm water, sunlight and something to feed on. One hot day is often what tips it over.
Common causes in Melbourne's west
- A hot day after a mild run. Point Cook and Werribee can swing from cool to a hot northerly in a day. Warm water and strong sun burn through chlorine fast.
- A storm or heavy rain. Rain dilutes the chlorine and washes in leaves, dust and garden debris that algae feeds on.
- The chlorinator isn't keeping up. Low salt, a scaled cell, or output still turned down from winter.
- The pump wasn't running. A power cut can reset the timer, or a tripped switch stops the pump without anyone noticing.
- A clogged filter or full baskets, so water isn't being filtered properly.
- Water out of balance. High pH makes chlorine work less well. Low stabiliser lets the sun break chlorine down quickly, and very high stabiliser can also slow it down.
- A busy weekend. Lots of swimmers, sunscreen and a party all use up chlorine.
How bad is it?
- Light green or teal, and you can still see the floor: early algae. Usually the quickest fix.
- Dark green, cloudy, and you can't see the floor: a full bloom. This takes longer and more work.
- Yellow or mustard patches on shaded walls: a different, stubborn type of algae that needs brushing and targeted treatment.
- Water turns clear green or brown straight after a big chlorine dose: metals in the water may be the cause, which needs a different treatment.
Safety first
Don't swim in a green pool. If you can't see the floor, keep children and pets away from it completely, because you can't see someone in trouble or anything sitting on the bottom. Check the gate is closed and latched.
If you treat it yourself, follow the label on every product. Keep chemicals in their original containers, store them apart, and never mix them. Acid and chlorine together can release toxic gas. Add chemicals to water, never water to chemicals. If you're unsure about any of it, call a professional.
The fix
This is what a green pool recovery involves. The details depend on how far gone the pool is.
- Test the water first, so the treatment matches the problem.
- Get the pH into range, so the chlorine can work.
- Brush every surface to break up the algae.
- Shock with a chlorine dose sized to the pool's volume and the readings.
- Run the filter continuously, and clean or backwash it often, because it fills with dead algae fast.
- For a full bloom, floc the water so the dead algae settles, then vacuum it to waste.
- Rebalance, check the chlorinator and run time, and retest over the next few days.
A mildly green pool can often be cleared in a day or two. A pool you can't see into can take several days and more than one visit.
When to call us
Call us if you can't see the floor, if you've shocked it and it's back within days, if you think the pump, filter or chlorinator is the cause, or if you'd rather not handle the chemicals. A pool that keeps turning green usually has an equipment or balance problem behind it, and that's what we look for.
How to stop it coming back
- Increase the pump run time as the weather warms.
- Turn the chlorinator output up for summer, and check salt.
- Test after hot days, storms and parties.
- Keep the baskets and filter clean.
- Keep pH and stabiliser in range.
Green today?
Book a green pool recovery and we'll test, treat and get it back to clear, with a visit report so you can see what we found. Then keep it that way with a Care Plan, with fortnightly visits from October to April, no lock-in and no exit fee. Book online or call 0476 476 080, Monday to Friday, 8am to 6pm.
