There’s nothing worse than opening your spa cover expecting clear, inviting water — only to find it looking green, brown, or even purple. Many spa owners assume this is algae, but that’s often not the case. Most of the time, coloured spa water is caused by metals in the water, not algae growth.

Understanding why this happens, how to fix it, and how to stop it from returning will save you time, money, and stress.

What Causes Coloured Spa Water?

Spa water that is technically “clear” but has a strange colour is usually the result of oxidising metals like iron, manganese, or copper. When you add chlorine, bromine, or any other oxidiser, these metals react and cause the water to change colour.

Here’s what different colours can mean:

• Yellow: Iron or manganese

• Brown or red: Iron or manganese

• Green: Copper

• Purple: Manganese, copper, or potassium

• Black: Manganese

Even if you’ve never had this issue before, it can suddenly appear because:

• Water composition changes over time – Seasonal rain, drought, or even seismic activity can shift mineral levels in your water supply.

• Council water works or hydrant flushing – When water mains are flushed, iron from old pipes can be loosened and carried downstream, ending up in your spa.

How to Fix Coloured Spa Water

The good news is that metal-related discolouration is treatable. Follow these steps:

1. Shock your spa water
   Add granular chlorine or bromine shock at a rate of 30 g per 1,000 L of water (or follow the directions on your spa shock product). This will oxidise the metals, making them easier to remove.

2. Wait 24 hours
   Allow your spa water to circulate. You may notice the colour darken before it clears — this is normal as the metals finish reacting.

3. Assess and repeat if necessary
   If the water is still discoloured after 24 hours, repeat the shock treatment. Multiple applications may be required if there’s a high level of metals present.

How to Prevent Coloured Water in the Future

The best way to avoid this problem is to stop metals from building up in your spa in the first place.

• Use a metal-removing product
  BioGuard Pool Magnet Plus and BioGuard Purity are excellent options. They bind to metals, keeping them from reacting with your sanitiser.

• Add after every top-up
  Any time you add fresh water, dose with a small amount of metal remover to maintain protection. This is particularly important if your water source is known to have high iron or manganese levels.

• Maintain balanced water
  Keeping pH and alkalinity in the correct range helps prevent metals from precipitating and staining your spa surfaces.

Why This Matters

Leaving metals untreated can not only cause discoloured water but also result in staining on your spa shell and fittings. Regular maintenance and using the right products will protect your spa’s finish and keep the water sparkling clear.

The Spa Shop’s Recommendation

At The Spa Shop, we see this issue frequently — especially after heavy rain or council water flushing. Our team recommends keeping BioGuard Pool Magnet Plus or BioGuard Purity on hand. These products are easy to use, safe for your spa, and highly effective at keeping metals under control.

Clear water isn’t just about appearance — it makes your spa safer and more enjoyable to use. If you’re dealing with discoloured water or want advice on preventing it, pop into The Spa Shop and we’ll help you get your spa back to perfect condition.