Aussie pools logo


Expert advice for pool owners

Black Spots in pool

Black Spot Algae

Black spot algae on pool surfaces is an issue that some pool owners have battled with over several years. This is because this form of algae is very resilient to normal levels of chlorine and brushing. Remember, it forms a biofilm over itself which protects it from the chlorine in the pool.  Because of this protective layer,  it is far more resilient and stubborn than normal green algae. Even once you remove the spots, they often return within a few months and start spreading in the pool once again.

How to remove black spot algae

  1. Vacuum and brush the entire pool surface, particularly where the black spot is present.
  2. Test the pool water and have the phosphates tested at your local pool shop.  Add what is needed to balance the water within the normal ranges.
  3.  Add 2 kgs of stabilized chlorine to the pool water and run the pump for 15 minutes while brushing the spots again.
  4. Add a good quality copper based algaecide to the pool, dissolve in a bucket of water first.
  5. Add a ployquat algaecide to the pool at the same time.

If you don’t have time to get all of these separately, these items are sold in kit form along with technical support here.  Make sure you use top-quality products when following these steps and cheap copper algaecides will stain the pool surface.

WARNING: Don’t acid wash your pool to remove black spot

While there are various ways to removing algae, we don’t suggest acid washing the pool. This is because black spot also lives in the pump, filter, and pipes. So even if acid washing removes it off the surface, once you refill it, the algae will simply blow back into the pool and start regrowing.  Acid washing is a waste of money and water.

vblack spot algae in swimming pool
Algae staining in swimming pool
black spot algae in swimming pool

Top 5 causes of black spot algae

There are several theories and ideas as to what causes and how to remove black spot algae. These include:

  1. Surrounding vegetation carrying black spots can fall into the pool and then this algae spreads in the pool. Also, a quick google search of ‘black spot on leaves and plants’ will reveal millions of websites discussing this issue.  Black spot is very common in the garden.
  2. Poor water maintenance will often result in the formation of black spots.  Low chlorine levels and an unbalanced pH are the main contributors to algae getting started in your pool.  
  3. High phosphate levels: Phosphates are nutrients that can feed algae. High phosphate levels in the pool water can make it easier for black spots to grow.
  4. Older pebble pools as they age will become more coarse to the touch.  This is because the cement that holds the pebbles together will erode away over time with pool water exposure.  This then creates deeper gaps between the pebbles that become a great hiding place for black spot algae to start growing and spreading.  
  5. Seawater. Some suggest it originates from seawater. However, this theory is not very credible as pool owners in Alice Springs experience black spot in their pool if it is not maintained correctly.  

Pool black spot remover – without draining

Shock chlorination, regular brushing, and a quality algaecide are sometimes successful approaches to removing black spot algae. If that is not working for you then other suggestions on how to remove black spots can be found here. Remember, whatever solution you try, make sure that it treats all of the pool water everywhere including the pipework and filter, not just in the main pool. Otherwise, the algae will be back within two weeks.  Contact us for more information.  Pictures supplied by:

Images of black spot algae

Algae in pool
Black spot algae often starts as green algae.
Algae staining in swimming pool
Green and black spot algae algae lead to surface staining.
Black spot in pools
Black Spot in Pebble Pool

Black spot in fibreglass pools

As a rule, it is very uncommon for black spot algae to form in fibreglass pools.  This is because it cannot attach in fibreglass pools because the surface of the pool is so smooth.  For this reason, black spot is not able to get properly embedded in your pool.  Because of this, it cannot grow in the pool.  Remember, the spots may look exactly like black spot algae but most times it is not an algae that you are seeing but mineral staining. 

In summary, black spots in fibreglass pools are either osmosis or mineral deposits from pool salts or algaecides.  These spots can usually be removed with stain treatment products.  Remember, it is very likely that an algaecide designed to kill black spots will do absolutely nothing at all to remove the spots in a fibreglass pool.

black spots in fibreglass pool

Metal stains often look like black spot algae

Many times pool technicians or pool owners mistake metal or copper staining for black spot.  This mistake is usually uncovered when they add an algaecide, or granular chlorine to the pool.  Doing this will often make metal stains worse rather than better.  The examples below show metal staining.  The images are NOT black spots.

Do these pools have black algae? (no they don't)

black spot in pools
copper staining in pool
Chlorine free pools with copper staining
Michelle Johnstone
Michelle JohnstoneMiami - Gold Coast
Read More
I had a issue with my new pebblecrete pool that was driving me nuts. These guys were really helpful and directed me to a descaling product that fixed it for me.
Stephen Sedgwick
Stephen SedgwickKellyville - Sydney
Read More
I had a large rust stain on the side of my pool that was growing quickly. It was not until I saw this website that I realised that it was coming from the reinforcing steel. Glad I stopped wasting money trying stain removers.
Stephanie Johanson
Stephanie JohansonToongabbie - Sydney
Read More
I was advised that my pool's interior needed replacement due to staining caused by Black Spot Algae. Thanks to the product sent by Aussie Pools, all the black spot was completely removed in just three weeks. I am extremely satisfied with their solution and so glad I don't need a new pool for no reason.

Final thoughts

Make no mistake, black spot algae is no joke.  Some websites even suggest that you can never get rid of it.   We have found that with the right products and process, you can remove black spot algae and keep it gone.  The trick is the use of enough of the right products to kill it off completely.  Don’t play around with it as it will become resilient to your attempts and become even harder to remove.  

If you are going to treat it then go all the way and do it properly.  Please contact us if you have any questions or are unsure about anything.  We are happy to help.