Understanding Algae: The Uninvited Guest in Your Pool
It starts innocently enough — a faint green hue in the shallow end, a slick patch on the tiles. Before long, your pristine pool, once a mirror to the sky, becomes a murky lagoon where algae have taken root. Anyone who’s maintained a pool even for a single summer knows how stubborn and opportunistic this invader can be. But what if we could stop it before it even began?
Algae may be persistent, but it’s also remarkably predictable. Like any living organism, it needs specific conditions to thrive: warmth, sunlight, still water, and a lack of sanitising agents. Knowing this gives us the edge, and if we act early — even before spring’s warm breath awakens the spores — we can keep our waters crystal clear and welcoming.
Think Like Algae: Timing Is Everything
In my early days of landscaping and outdoor pool care, I would wait until I saw visible algae to take action — and I always regretted it. These days, I start my algae prevention routine the moment frosts start to retreat. The trick is to anticipate the bloom, not chase it down.
A good rule of thumb: when average daytime temperatures start to hover consistently above 15°C (around 59°F), it’s time to shake hands with your pool tools and get to work.
Circulation: Keep the Waters Dancing
Still waters might run deep, but in a swimming pool, they also signal stagnation. And stagnant water is algae’s favourite home. Ensuring your circulation system is functioning efficiently is perhaps the most crucial — and most overlooked — aspect of algae prevention.
Make sure your pump is running at least 8 to 12 hours a day during the warmer months. Check that the jets are angled to encourage a circular flow, and don’t forget the little nooks — steps, corners, and behind ladders — where stagnant water loves to linger.
I once worked on a garden pool nestled against a laurel hedge. It was beautiful but shaded on one side, and circulation was lacking near the steps. No matter how much chlorine we added, algae returned — until we adjusted the return jets and added a secondary jet near those stubborn corners. Since then, algae’s been given the boot.
Brushing: A Gentle Morning Ritual
I like to start my pool maintenance the way one might begin a walk through a dew-touched garden: with a gentle brushing of the surfaces. Brushing the walls and floor of your pool disrupts microscopic algae spores before they settle and form colonies.
Use a brush suitable for your pool’s surface — softer bristles for vinyl or fibreglass, more robust ones for concrete or plaster. Focus on:
- Steps and ladders
- Waterline and tile grout
- Pool corners and low-circulation zones
If you make this a weekly habit, not only will you keep biofilm at bay, but your pool will also sparkle in a way that photographs simply don’t do justice.
Sanitiser Levels: Not Just Chlorine, But Consistency
Imagine attempting to water your garden with a watering can that leaks — no matter how much water you pour in, it never quite reaches the roots. That’s what inconsistent sanitiser levels do to your pool. One moment, they fight bacteria and algae; the next, they vanish with sunlight or rain, giving algae the freedom they crave.
You’ll want to maintain a free chlorine level consistently between 1 and 3 ppm (parts per million). In the height of summer, during heavier usage or after rainstorms, test daily. A simple drop test kit or digital photometer makes this easy and even, dare I say it, enjoyable — especially if you imagine each test as a dialogue with your pool.
For those using saltwater systems, be sure your chlorine generator is working correctly and doesn’t need a cell cleaning. A faltering salt system is a silent invitation to algae.
Phosphates: A Feast for the Green Foe
Here’s a lesser-known tip that changed the way I thought about algae: they love phosphates. Phosphates serve as a food source, and they enter your water through leaves, runoff, even certain pool chemicals. Keeping them low is like removing a buffet table before your guests arrive.
Test your phosphate levels monthly. If they creep above the 500 ppb (parts per billion) mark, it’s time to consider a phosphate remover. These are widely available in liquid form and are easy to add — typically poured straight into the skimmer while the pump is running.
After adding, allow the system to circulate continuously for 24 hours. You may notice the water go slightly cloudy as the product binds to the phosphate, but this should clear within a day.
Covers: Friend or Foe?
Pool covers are a double-edged sword. On one hand, they reduce evaporation and keep debris out; but on the other, if improperly used, they trap heat and limit circulation — creating exactly the environment algae dreams of.
If you use a cover, especially a solar one, be sure to remove it regularly — daily if possible — to allow gas exchange and light exposure. Brush the underside weekly, and store it dry and out of direct sun when off the pool to prevent mould and algae accumulation.
I’ve seen impeccable pools turn green simply because a solar cover was left on too long after a heatwave. A well-used cover is a boon; a forgotten one is a risk.
UV and Ozone Systems: Silent Allies
If your approach to your outdoor space is driven by sustainability or a desire to limit harsh chemicals — as more and more of my clients are — consider adding secondary sanitising systems. Ultraviolet (UV) and ozone systems can significantly lower your chlorine needs, all while attacking pathogens at the cellular level.
They’re not a replacement for chlorine, but they are an excellent line of defence, especially in larger pools or pools under consistent use. They’re also effective at reducing chloramine build-up and that distinctive “pool smell.”
While the upfront cost is steeper, the long-term clarity and reduction in chemical needs can be well worth it — like switching from disposable razors to a fine steel blade. A subtle improvement, but one felt through every stroke.
Landscape Management: The Green Around the Blue
Algae doesn’t just come from within — often, it’s the garden around your pool that plays the hidden antagonist. Overhanging trees dropping organic matter, wind-swept mulch entering the water, or even splashing runoff from a nearby bed of fertilised flowers can introduce nutrients and spores into your pool.
To help keep things tidy and algae-resistant:
- Trim trees and shrubs to reduce debris
- Use gravel or hardscape near the pool perimeter instead of mulch
- Install a drainage swale or barrier to redirect runoff
One of my favourite garden pool installations used lavender and thyme as border plants — not only were they pleasant aromatically, but they were also low-shedding and naturally pest-repellent. Harmony, it turns out, can be both scented and strategic.
The Value of Routine: A Garden of Clear Water
Ultimately, algae prevention isn’t a one-time project—it’s a rhythm, a quiet dance with your surroundings. It’s the early morning testing, the careful brush strokes, the alignment of jets, and the watchful eye on the skies above. Like any healthy garden, a pool flourishes when tended with diligence and love.
There’s a certain joy, I think, in looking out across a shimmering surface that reflects not just the clouds above, but the care beneath. Algae may always be waiting, but with preparation and patience, it need not be a guest this season — or any after that.
And so, before that first warm week of spring, I invite you: walk out to your poolside, take a seat under whatever tree you’ve come to know best, look across the surface, and make your quiet pact with the water. Together, you’ll keep the green where it belongs — in the garden beds, and not between the tiles.
