Skip to content

How to Treat Mustard Algae

In this article, we show you how to spot and treat Mustard Algae and other resistant algae strains in your swimming pool.

Thankfully this type of algae does not occur regularly, however, it can be quite stubborn to treat as it is resistant to conventional chlorine treatment.

Pool owners can often think that their pool cleaner is not operating correctly as it fails to collect the "dirt", when in fact it is this pesky Mustard Algae. This cannot be collected by a pool cleaner. It will simply go through the cleaner and/or filter and return soon after. This pool problem must be treated with chemicals.

Signs of mustard algae

Mustard Algae will present differently from regular algae problems. Below is a list of signs you have mustard algae (or yellow algae) in your pool

  • Looks like there is fine sand at the bottom of your pool
  • Has a yellow or brown appearance
  • It is not slimy
  • You will notice the algae on your pool walls and steps
  • Appeared quickly and fast growth
  • Appears on pool toys, pool cleaners and other pool equipment
  • Can be easily brushed away (but will grow back quickly)
  • Cloudy water
  • Stains on your pool lining or surfaces


Is Mustard Algae harmful to humans?

While mustard algae itself does not pose a risk to humans, it does however devour chlorine making it difficult to maintain healthy levels of sanitation in your pool water. This then increases the risk of harmful bacteria growth. Bacteria such as e.coli can thrive in an environment that is overrun with Mustard Algae.

Steps to get rid of Mustard algae

This treatment is also beneficial for stubborn algae outbreaks, or if your pool has turned green. Ideally, you will start treatment as soon as you notice the fine sand/dirt appearing on the pool floor or other surfaces. Early treatment will have a faster outcome.

The following treatment is broad-spectrum and recommended for all mutant algal strains.

  • Vacuum your pool to waste. If you don’t know how to do this - please message us and ask
  • Clean your pool filter. Backwash or hose cartridges. This is necessary as the algae will thrive in your filter
  • Adjust pool pH to 7.2-7.6 - If this is necessary, filter for 4 hours before proceeding to the next step
  • Add 1 x clarifier cube into the skimmer box
  • Add liquid chlorine
    • 10L for pool up to 20kL
    • 15L for pools between 20kL and 55L
    • 20L for pools between 55kL and 70kL
    • 30L for pools between 70kL and 100kL
  • Brush pool walls vigorously. This is very important. Keeping the algae suspension is the best way to get rid of it.
  • Filter for 7 hours then add
    • 1 x Algae killer for pools up to 20kL 
    • 1 x Hotzone for pools between 20kL and 70kL
    • 2 x Hotzone for pools between 70kL and 110kL
  • Run pool filter 24 hours a day until water clarity has reestablished (may take 2-4days), backwash filter and brush pool once a day.
  • Test your water regularly to rebalance pool water

In fibreglass and vinyl pools, any algae should be gone in one week

For concrete and pebble pools, it may take up to 3 weeks with continuous brushing and high chlorin to complete remove the algae


Treating stubborn algae is time-consuming and costly. So it is always best to look toward prevention rather than cure.

To prevent a resurgence of mustard algae, it is important to test your pool regularly - particularly in Summer and when it is being used often.

It is during these periods that you may need to top up pool water with chlorine or apply a regular shock treatment.


Prev Post
Next Post
Someone recently bought a
[time] ago, from [location]

Thanks for subscribing!

This email has been registered!

Shop the look

Choose Options

Edit Option
this is just a warning
Product Enquires
Shopping Cart
0 items

Before you leave...

Take 20% off your first order

20% off

Enter the code below at checkout to get 20% off your first order


Continue Shopping