Why are there stains on my pool ?
Pool stains can have several different causes, and identifying the type of stain is the first step towards choosing the correct treatment. The most common types of stains found in Queensland pools are algae stains, organic stains, metal stains, and calcium scale.
Algae stains
Algae are common cause of staining in Queensland pools and are usually the result of low chlorine levels, poor filtration, or poor water circulation.
The most common types include:
Green algae – causing green patches or a green pool.
Mustard algae – yellow or mustard-coloured patches that often appear in shaded areas.
Black spot algae – dark black spots that grow into the pool surface and are much more difficult to remove.
Organic stains
Organic stains are caused by leaves, branches, fruits, flowers and other organic debris sitting on the pool surface for an extended period.
They are usually brown, green or grey stains.
Light stains can often be removed by brushing, while more stubborn stains may require a specialised stain remover.
Metal stains
Metal stains occur when dissolved metals in the water react with your pool chemistry and settle onto the pool surface.
The most common metal stains include:
Iron stains – usually brown or rust-coloured. Iron is naturally present in many pool salts, particularly lower-quality or less refined salts. These stains often first appear in front of the return jets before spreading elsewhere.
Copper stains – typically dark blue or black. They are commonly caused by copper ionisers (freshwater systems), copper-based algaecides, or corrosion of copper equipment.
There are also other types of metal staining found in Queensland pools, each requiring a specific treatment depending on the metal involved.
Calcium scale
Calcium scale isn't technically a stain, but it is often mistaken for one. It appears as a rough white or light grey deposit on pool walls, tiles, waterlines and floors.
It forms when the calcium hardness, pH or total alkalinity are too high, causing calcium to come out of the water and stick to pool surfaces and equipment.
Alex’s Advice💡
Every stain is different, so there isn't a single treatment that works for them all.
Algae stains are treated using chlorine and proper water balancing.
Organic stains are usually treated with specialised stain removers or by oxidation.
Metal stains require metal-specific stain treatments and careful water balancing.
Calcium scale is removed using scale removers, mechanical cleaning, or acid washing in severe cases.
For most metal stain treatments, the pool's chlorine level must be reduced to zero before treatment can begin. This is why winter is generally the best time to carry out stain removal, as lowering chlorine levels is less likely to generate algae bloom.
Algae should be treated as soon as it appears, as it spreads quickly if left untreated. Unlike other stains, algae require a chlorine-based treatment and can be treated at any time of the year.
If you're unsure what type of stain you're dealing with, feel free to book a stain assessment. Correctly identifying the stain before treating it can save both time and money while preventing unnecessary damage to your pool.