Black Spots in pool

Black spots in pool surfaces is an issue that some pools owners battle 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,  it is far more resilient and stubborn than normal green algae. Even once it is removed, it often returns within a few months and start spreading in the pool once again.

"Black Spots in pools is the toughest and most resilient of all the algae types. Many pools that have black spot often have water that is perfectly balanced. To remove black spot a high strength black spot algaecide is required. This is why it so often very hard to remove and very often returns later"

vblack spot algae in swimming pool
black spot algae in swimming pool

Black spots in pool – Main causes

There are several theories and ideas as to what causes and how to remove black spot algae. Some suggest that surrounding vegetation carrying black spot 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.

On the other hand, others believe that it originates from seawater. However, this theory is not very credible as pool owners in Alice Springs experience black spot in there pool if it is not maintained correctly.  Whatever the cause of black spot, the best way to keep it away is to maintain your pool water.

Don’t acid wash your pool

While there are various approaches to removing algae, it is not recommended to acid washing the pool. This is because black spot hides in the pump, filter and pipework. So once you refill the pool, the algae will simply re-enter the pool. Remember, in this case, acid washing is a waste of money and water.

Pool black spot remover – without draining

Shock chlorination, regular brushing and a quality algaecide are often successful approaches to removing black spot algae. Some other suggestions on how to remove black spot can be found here. Remember, whatever solution you try, make sure that it treats all of the pool water everywhere, not just in the main pool. Otherwise, the algae will be back within two weeks. Finally, keep in mind that the algae can live in the pipework and filter.

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 a fibreglass pools.  This is because black spot 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 black 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 be usually be removed with stain treatment products.  However, don’t be fooled, it is very likely that an algaecide designed to kill black spots will do absolutely nothing at all to remove the spots.

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 algae.  This mistake is usually uncovered when they add an algaecide 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 in pool surfaces from algae.

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

black spot in pools
copper staining in pool
Chlorine free pools with copper staining