Phosphates in Pools: The Hidden Algae Fuel You Need to Control

Your pool looks clean, chlorine levels are perfect, pH is balanced – yet algae keeps returning. You're constantly adding extra chlorine, brushing, and fighting a losing battle. The culprit might be invisible: phosphates. These nutrients act as fertiliser for algae, turning your pool into an all-you-can-eat buffet for unwanted green growth. Understanding and controlling phosphates is increasingly recognised as essential for Australian pool maintenance, particularly during our long, warm swimming seasons.

What Are Phosphates?

Phosphates are compounds containing phosphorus that dissolve in pool water. They're completely invisible – you can't see, smell, or feel them. Algae and other aquatic organisms use phosphates as a primary nutrient source for growth. The more phosphates in your water, the easier it is for algae to establish and thrive, even when chlorine levels seem adequate.

Ideal phosphate levels are below 100 ppb (parts per billion). Between 100-500 ppb, you'll notice increased algae susceptibility. Above 500 ppb, you're fighting an uphill battle – algae blooms become frequent and increasingly difficult to control.

Common Sources of Phosphates

Fertilisers and Garden Runoff

This is the biggest contributor for most Australian pools. Lawn fertilisers, garden beds, and potted plants around your pool area contain high phosphate levels. When it rains, irrigation runs, or you water gardens, phosphate-laden water can splash or drain into your pool. Even small amounts accumulate over time. Pools surrounded by well-maintained lawns and gardens are particularly vulnerable.

Organic Debris

Leaves, grass clippings, pollen, bird droppings, and insects all contain phosphates. As this organic matter breaks down in your pool, it releases phosphates into the water. Australian pools, especially those surrounded by native vegetation or under deciduous trees, constantly battle organic debris. That beautiful tree providing shade is also providing phosphate fuel for algae.

Bore Water and Fill Water

Some water sources naturally contain phosphates, particularly bore water in agricultural or former agricultural areas where fertiliser use has contaminated aquifers. Perth and regional Western Australian bore water can contain measurable phosphate levels before you've even used the pool. Even scheme water in some areas contains trace phosphates from agricultural runoff in catchments.

Swimmers

Body lotions, sunscreens, cosmetics, hair products, and sweat all introduce phosphates. A busy pool party can add significant phosphates in a single afternoon. The more swimmers and the more products they're wearing, the higher the phosphate load.

Some Pool Chemicals

Certain pool chemicals, particularly some older algaecides and cheaper clarifiers, contain phosphates as inactive ingredients. Ironically, products meant to clear your pool can contribute to future algae problems. Always check product labels and choose phosphate-free formulations when available.

Detergents and Cleaning Products

Washing pool toys, equipment, or even yourself with phosphate-containing soaps before entering the pool introduces phosphates. Residues from cleaning pool surrounds that wash into the water also contribute.

How Phosphates Fuel Algae Growth

Think of phosphates as algae food. Algae need three things to thrive: sunlight (abundant in Australia), nutrients (phosphates and nitrates), and water. You can't eliminate sunlight or water, but you can control nutrients. Even with adequate chlorine, high phosphate levels give algae the nutrition they need to grow faster than chlorine can kill them. This is why you can have "proper" chlorine levels yet still battle persistent algae blooms.

Signs Your Pool Has High Phosphates

You can't see phosphates directly, but you'll notice their effects:

• Recurring algae problems despite proper chlorine levels
• Algae returning quickly after treatment
• Cloudy water that doesn't respond well to normal treatments
• Excessive chlorine demand – constantly needing more chlorine than expected
• Difficulty maintaining clear water during warm weather
• Green or mustard algae appearing in the same spots repeatedly

Testing for Phosphates

Standard pool test strips and kits don't measure phosphates. You'll need a specific phosphate test kit (available at most pool shops) or have your water professionally tested. Most quality Australian pool retailers offer comprehensive water testing that includes phosphate levels. Test at the start of swimming season and whenever you're experiencing recurring algae issues.

Treating High Phosphate Levels

Phosphate Removers: How They Work

Unlike cyanuric acid or sulphates, phosphates can be chemically removed from pool water. Phosphate removers contain compounds (typically lanthanum-based) that bind to phosphates, creating particles large enough to be filtered out. The phosphates don't disappear – they're converted into a form your filter can capture and remove.

Clearchem Starver: The Australian Solution

Among phosphate removers available in Australia, Clearchem Starver stands out as a particularly effective option. Developed specifically for Australian conditions, Starver uses advanced lanthanum technology to eliminate phosphates quickly and thoroughly. What makes Starver a winning choice for Australian pool owners is its concentrated formula – a little goes a long way, making it economical despite our typically larger pool sizes.

Starver works by forming microscopic particles that bind phosphates, which your filter then removes. It's compatible with all pool types – chlorine, salt, mineral, and even natural pools. Unlike some phosphate removers that cloud your water for days, Starver typically clears within 24-48 hours with proper filtration.

Application Method

Calculate the required dose based on your phosphate test results and pool volume. Pour Clearchem Starver around the pool perimeter with the pump running. Your water will initially become cloudy or milky – this is normal and indicates the product is working. Run your filter continuously for 48 hours, then backwash or clean your filter thoroughly to remove the phosphate particles. Retest phosphates after 72 hours to confirm levels are below 100 ppb.

Filter Maintenance is Critical

The phosphate-lanthanum particles must be removed through filtration. If you don't run your filter long enough or clean it afterward, phosphates can reintroduce into your pool. After treatment, backwash sand or DE filters thoroughly, or remove and clean cartridge filters. This step is non-negotiable for successful phosphate removal.

Prevention Strategies

Manage Surrounding Environment

Create barriers between garden beds and your pool. Ensure irrigation and rainfall drain away from the pool, not into it. Consider phosphate-free fertilisers for gardens near your pool. Regularly skim leaves and debris before they sink and decompose. These simple landscaping and maintenance habits prevent phosphates from entering in the first place.

Shower Before Swimming

Encourage swimmers to rinse off sunscreen, lotions, and products before entering. A quick shower removes most phosphate-containing residues. This is particularly important after pool parties or when children have been playing outdoors.

Regular Testing

Test phosphates at the start of each swimming season and monthly during peak usage. Catching elevated levels early (200-300 ppb) is far easier to treat than waiting until you're at 1,000+ ppb and battling constant algae.

Choose Phosphate-Free Products

Select pool chemicals labelled phosphate-free. Many modern algaecides, clarifiers, and other treatments now advertise this specifically because phosphate awareness is growing among pool owners.

Maintain Proper Water Balance

While phosphate control is important, it's not a substitute for proper chlorination and water balance. Think of it as an additional tool in your arsenal. Proper chlorine levels, balanced pH, and good filtration combined with low phosphates create an environment where algae simply can't thrive.

Australian Climate Considerations

Our long swimming seasons, intense sunlight, and outdoor lifestyle make phosphate management more critical than in cooler climates. Pools see more use, collect more organic debris, and receive more sunscreen and body products. Additionally, many Australian homes feature extensive gardens and lawns around pools – beautiful, but potentially phosphate-rich environments.

Coastal areas face additional phosphate challenges from salt spray containing organic matter. Regional areas using bore water for gardens may inadvertently introduce phosphates when overspray or runoff enters pools.

Cost-Benefit Analysis

Phosphate removers like Clearchem Starver represent an upfront cost, but consider the alternative: constant algaecide treatments, excessive chlorine use, frequent shocking, wasted time brushing and vacuuming, potential equipment damage from algae-related pH swings, and the frustration of never quite achieving crystal-clear water. One or two phosphate treatments per season typically cost less than repeatedly fighting algae blooms.

When Phosphate Removal Isn't Enough

Phosphate removal is powerful but not magic. If you still have algae after reducing phosphates below 100 ppb, look for other issues:

• Inadequate chlorine levels or inconsistent chlorination
• Poor circulation creating dead zones
• Inadequate filtration time or dirty filter
• High cyanuric acid blocking chlorine effectiveness
• pH or alkalinity imbalances
• Nitrates (another algae nutrient) requiring dilution

Fun Fact: A single gram of phosphate can support the growth of up to 100 grams of algae! That's a 100:1 nutrient-to-algae ratio, which explains why even seemingly small phosphate levels (500 ppb equals just 0.5 grams per 1,000 litres) can fuel massive algae blooms. In a typical 50,000-litre Australian backyard pool with 500 ppb phosphates, you have enough phosphate to theoretically support 2.5 kilograms of algae growth. No wonder that green bloom appeared seemingly overnight!

The Bottom Line

Phosphates are the hidden factor behind many persistent pool problems. They enter from numerous sources – fertiliser runoff, organic debris, swimmers, and even some pool chemicals – and accumulate silently until algae explodes across your pool. Unlike some pool chemistry challenges, phosphates can be effectively removed using quality products like Clearchem Starver.

Test your phosphate levels if you're battling recurring algae despite proper maintenance. One treatment often solves problems that months of increased chlorination couldn't touch. Combined with prevention strategies – managing runoff, skimming debris promptly, and choosing phosphate-free products – you can maintain phosphate levels that starve algae rather than feeding it.

Australian pool owners face unique challenges with our climate, landscaping practices, and outdoor lifestyle. Understanding phosphates and incorporating phosphate management into your routine gives you another powerful tool for maintaining that crystal-clear water we all want. Stop fighting algae endlessly – remove the fuel source instead.