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Beach Ball in Pool

Stain Removal

Staining on pool and spa surfaces is common and can result from a number of mineral and organic sources. The SeriouStain range provides a broad spectrum treatment for large stains, or SPOTBLOC™ for smaller stains.

Identifying your stain will help prevent future staining

Staining may be localized to a small area, be wide spread through the pool, reoccur at certain times during the year or appear infrequently. As such, identifying and treating the causes of stains, will help prevent the stain from simply reappearing after treatment. 

Pool Stain Chart Algaefree Australia


Smaller spot stains may not require a whole-pool water treatment. SPOTBLOC™ stain eraser contains a special blend of acids, suitable for any pool surface, in an easy to use reusable chalk.

Simply rub a thin layer or place the block directly onto the stain, above or below water, to treat. Check the stain periodically and reapply if necessary. The block will not dissolve quickly and can also be used to remove stains on other stone surfaces. Simply dampen the area with water and apply SPOTBLOCas described above.

No pH adjustment or water-balancing necessary.  

This is ideal for removing waterline scum, rust stains and organic marks from plant debris.


Larger, wide spreads stains demand the need for a whole-pool SeriouStain Remover treatment. Follow the guide below to get your pool looking its best again. 



Adjust chlorine level to 0.

  • Chlorine interferes with the acid treatment, so its important to either wait for chlorine levels to drop to zero, or adjust to 0 using additives.

Adjust to pH 7

  • Regular pH should range from 7.2 - 7.6, however, stain removal is most effective at a lower pH.

  • Treatment is most effective at a lower pH

  • In a 50,000 litre pool, approximately 2 litres of hydrochloric acid will adjust the pH from 8 to 7.

Turn off any chlorinator, ioniser, ozonator or UV systems

  • These systems may interrupt the treatment.



For recent stains:

In pools, add 250g of SeriouStain™ Remover per 10,000 litres of water (1.25 Kg per 50,000 litres). Dissolve in a bucket of pool water and our in around the edges. In spas, use 100g per 2000 litres.

Brush the walls and floor. If stains are gone after 24 hours, restore pH to 7.2 with a similar quantity of bi-carbonate of soda. 

If stains persist, see severe and old stains treatment.

For older, stubborn stains:

Add SeriouStain Remover at double the above dose (2.5 Kg per 50,000 litres). The option of additional hydrochloric acid pre-dissolved in a bucket of water may be added to further lower the pH and further dissolve tough stains. For:

  • Vinyl Pools- 500ml hydrochloric acid per 10,000 litres of ool water.

  • Fibreglass Pools- 1 litre of hydrochloric acid per 10,000 litres.

  • Concrete Pools- 2 litres of hydrochloric acid per 10,000 litres for white render, pebblecrete and colour quartz finishes.

  • For painted pools in good condition, use the dose for fibreglass.

Turn on pool pump for a few hours each day to circulate the water.

Most dark marks, stains or coloured streaks fade completely in 2-3 days, which is the maximum recommended treatment period for all pools.

Once stains and mineral deposits are completely removed, restore pH to 7.2 with sodium bicarbonate. Pre-dissolve 2Kg doses of sodium bicarbonate in a bucket of pool water and pour around the edge of pool at hourly intervals with the filter running. Check the pH between doses.

As a guide, 1 Kg of sodium bicarbonate will be required for each 1 Kg of SeriouStain Remover or 1 litre of hydrochloric acid used during treatment.



Replacing at least one third of the pool water with fresh water is recommended where high mineral levels are present. This dilutes the hardness of the water and prevents future mineral deposits in swimming pools.

Add a container of SeriouStain™ Inhibitor, which is a powerful blend of complexing (chelating) agents, tion and prevent such deposits from returning.

Related products

Stain Removers
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