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Black algae is just about the most stubborn algae to eliminate but don’t worry it can be done. The first thing you need to do is check that all your levels are correct, Chlorine, pH, Hardness and Stabiliser (see Water Chemistry).

If your home test kit does not read all of these then take a sample to your pool shop and have them test it.  

Add an algaecide once your levels are OK. Black algae are very chlorine resistant you need to add an algaecide to the water to offer another angle of attack. Algaecides are specifically designed to kill and prevent algae. So it’s a good idea to have an Algaecide in the water at all times. If you have black algae and haven’t got an Algaecide in the water now, you’d better put one in right away. For best results pour the Algaecide directly on to the affected areas.

 “Shock” the Pool: When shocking the pool with chlorine you must only use Calcium Hypochlorite or Sodium Hypochlorite. These 2 products are strictly chlorine and nothing else. It is also a good idea to add your shock dose closest to the most affected areas and in the evening.

 Brush the Walls: Black algae grow a protective barrier around themselves, so you will need to brush the affected areas really hard with a stiff brush to remove this barrier and then the chemicals (Chlorine and Algaecide) can do their job. If you have a Liner Swimming Pool make sure that the brush is suitable for vinyl surfaces.

 Improve Water Circulation: Black algae usually turn up in areas where there is lack of water circulation, do your best to direct your water return jets in a way that moves the most amount of water around. If you can direct the jets to make a whirlpool effect then you will have maximum movement.

Attack Black Algae head-on: As previously stated, black algae form a protective barrier around themselves, so you will have to regularly brush off the top of the algae and add your chlorine while it is exposed. Another tip is to sprinkle chlorine granules directly onto the affected areas and let it sit and burn off the algae, be careful if you have a liner as you could end up bleaching it. You can also rub a chlorine tablet onto the algae after you have brushed it (Make sure you wear non-porous gloves).

 Rinse and Repeat: Just keep testing and adjusting the water, scrubbing the black algae and adding chlorine as close as you can get it. You will eventually get rid of it! It will go, but it will depend on how bad the algae is as to how fast it will go. Water balance and scrubbing is the best thing you can do.