What To Do When I Have a Greenish Pool
Your pool isn't a swamp. It's not that green. But it's not right either, there's a tint to it, the water looks a bit hazy and you can't quite put your finger on why. This is actually the best possible time to deal with it. Catch a greenish pool early and it's usually a quick fix. Leave it, and you're looking at a full green pool recovery instead.
Here's how to work out what's actually going on, and what to do about it.
The short answer: a greenish (not fully green) pool is usually early-stage algae, metal staining from copper or iron or mustard algae clinging to shaded surfaces. Brush a wall for 30 seconds, if a green cloud lifts off, it's algae; if nothing changes, suspect metals. Catch it at this stage and it's a quick fix, not a full green pool recovery!
First, Figure Out What's Actually Causing Your Greenish Pool
Most people see green and reach straight for chlorine and algaecide. That's the right move if it's algae, but a slight green tint has three common causes, and they don't all get fixed the same way:
Early-stage algae. Chlorine dropped too low for too long and algae's getting a foothold before it fully blooms.
Metal staining. Dissolved copper or iron in the water, often from an old heater, a copper-based algaecide, or bore or tank water used to top up the pool, can tint water green when it reacts with chlorine.
Mustard algae. A yellow-green film that clings to walls and shaded areas rather than floating through the water.
Treating the wrong one wastes time, and in the case of metals, can actually make the colour worse.
Quick Ways To Tell Which One You've Got
Brush a small section of wall for 30 seconds. If a green cloud lifts up into the water, that's algae. If nothing happens and the tint stays exactly the same, it's more likely metals.
Feel the walls and steps. Algae feels slick or slimy, because it's a living film. Metal staining feels smooth and clean, even though the water around it looks tinted.
Think about timing. Turned green within hours of adding chlorine or shock? That points to metals, chlorine oxidises dissolved copper or iron and the colour shows up fast. Turned green gradually over a few days while your chlorine's been struggling? That's almost certainly algae.
Check where the colour is. Floating through the whole pool and clouding the water: algae. Clinging to shaded walls, ladders, corners or under equipment while the water itself stays fairly clear: likely mustard algae.
If It's Early-Stage Algae
Good news: caught early, this is a light job compared to a full green pool clean.
Test and rebalance pH first (aim for 7.0-7.4).
Give it a moderate shock - you don't need the aggressive dose a fully green pool needs.
Brush the walls, steps and corners to knock algae off surfaces before it spreads.
Run the filter for longer than usual for a day or two.
Retest the next day. If it's cleared, you're done. If it hasn't, you've likely got a bigger bloom on your hands than it first looked.
If It's Metal Staining
Don't just add more chlorine - that can intensify the colour rather than fix it. Metals need a metal sequestrant to bind the copper or iron so it can be filtered out, not oxidised further. It's also worth figuring out the source: an ageing copper heat exchanger, a copper-based algaecide, or a recent top-up with bore or tank water are the usual culprits. If you're not sure, this is a good one to bring a sample in for.
If It's Mustard Algae
This one's more stubborn than it looks. Because it clings to surfaces and develops a bit of a protective layer, normal chlorine levels often don't touch it. Thorough brushing of every affected surface, combined with a proper shock dose, is usually what it takes. Skip the brushing and you'll likely be treating it again in a couple of weeks.
When To Just Get It Checked
If you've brushed, tested and treated and it's still off after a day or two, or it keeps coming back, it's worth getting a second opinion rather than guessing with more chemicals. Free water testing is available in-store any time, no booking needed, or if you'd rather someone just sort it, our Green Pool Recovery service handles all three causes, not just algae.
Keeping It From Happening Again
A greenish pool is almost always a sign chlorine dropped somewhere it shouldn't have, or something's slowly building up in the water. Regular servicing catches both before they show up as colour change, which is a lot easier than treating it after the fact.
Need a Hand?
Get in touch or call us on 07 2812 2461 — we service Brisbane's southside, Redlands and Bayside and can tell you exactly what you're dealing with, not just guess.
Pool Wizard is a Brisbane-based pool servicing company and pool shop, servicing homes, strata properties, and real estate across Brisbane's southside, Redlands, and Bayside.
