How to Get Rid Of Blackspot Pool Algae

Black algae is perhaps the most difficult algae to get rid of! It has very deep roots that can grow into the side of plaster or concrete pools. It also has many layers that protect it from regular chlorine levels. You will usually find black algae clinging to your pool walls or steps in very shady spots. In order to get rid of blackspot pool algae, you must be aggressive!

Step-by-Step Guide to getting rid of stubborn black algae

Warning: Be prepared to do a lot of brushing. We suggest buying a good quality brush for this procedure.

1. Check the Water Chemistry In Your Pool

Make sure your pH levels always sit between 7.4 and 7.6 and your alkalinity levels are between 120 and 150 ppm (parts per million). If you're getting rid of blackspot algae, keep your pH lower at around 6.8 to 7 for 2 to 3 months. Algae loves high pH, so this will slowly kill it and its roots over time.

2. Brush the Pool Surface

We cannot stress brushing the pool surface enough. This will be the key to getting rid of black algae. Brush hard, brush thorough and brush often. Black algae forms a membrane which needs to be broken for treatment to work.

Brush the walls and floors with a steel bristle brush or a stiff plastic bristle brush for plaster pools.

3. Keep Your Chlorine Levels Nice and High

You're going to mainly be focusing on adding hydrochloric acid to your pool to lower your pH, but that, of course, goes hand-in-hand with making sure that your pool is sanitised with chlorine to help kill off the algae.

The use of an algaecide not only helps remove algae infestations but also starves them out to prevent algae colonization and blooming.

4. Brush Your Pool Again and Again

Brush your pool at least 3 to 4 times a week, concentrating on where you first spotted the algae. Remember, black algae has deep roots that can be embedded into your pool walls. It may look like it’s gone, but it’s probably still there. Just keep brushing. Continue brushing for several days after you see it starting to dissipate.

This is, however, not a guarantee. Black algae is relentless and could continue to infect your water. If it does, you know how to kill it, just be more aggressive next time. Perhaps consider an additional dose of acid and chlorine and constant brushing.

Don't forget to use some Black Spot Remover to make sure that the not only does the black algae brush off easier, but they stay off as well.

5. Vacuum Any Waste

To prevent any spores from recirculating into the filtration system, vacuum any debris on the floor of the pool. This is a rather lengthy topic so we've created an article dedicated just for manually vacuuming your pool, be sure to take a look at it for detailed instructions, tips and tricks, and how to save time and effort when manually vacuuming your pool.

6. Clean Your Filter

At the completion of your water treatment, thoroughly clean your filter. This includes manually washing your cartridge filter or back washing your sand filter.

Your filter is one of the places where black algae can hide in as it is hidden from direct sunlight. Black algae spores clinging to your filter can circulate around your pool making all your scrubbing useless. Give your filter a good soak in filter cleaner to make sure that all traces of the algae are gone for good.

How to Prevent Black Algae Growing

Keeping your pool properly balanced and sanitised is the key to keeping all forms of algae from growing. Make sure you:

  • Keep your pH, alkalinity and chlorine levels in the correct range at all times
  • Run your pump and filter for 8 to 12 hours a day all season long
  • Keep your pool clean by regularly vacuuming and brushing
  • Always have the required pool chemicals on hand. Algae can bloom overnight and they replicate very fast. At the first sign of algae growth, do the required pool treatments!


More resources on how to keep your pool free from black algae

The article above is meant to be a general guideline on how to remove black spot algae. For more details on the individual steps, check out the blog posts below.

How to test and fix your pool water! (Testing your water chemistry)

How To Get Rid Of Pool Algae (Green Pool Water)

How to backwash your sand filter! (Cleaning your filter)

How to fix cloudy pool water (Treatment for ALL algae types)

How To Get Rid Of Mustard Algae (Another type of Algae)

Featured Products throughout this blog

Do you have any questions about this topic or the featured products? No worries, we're here to help! Drop us a question down below and we'll get back to you ASAP.

Happy swimming :)

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