How to get rid of black algae

Black algae attack – how I got rid of it some years ago:

Here’s an unedited entry from my diary in July 2007 when I had black algae outbreak in a 10×5 metre pool of classic tiled concrete construction:

“With pump off, I brushed off every bit of black algae that I could see. This took more than 3 hours of hard scrubbing. Whilst doing so I dropped shock chlorine onto the floor in the position where I was working and also used a chlorine tablet on the bottom of the pool, which I placed over really stubborn marks after brushing them. I then went back to the stubborn marks and brushed again until it was all gone. In total I put in 20g/cubic metre 1.5kg in total into the 75 m3 pool. This should have raised the level of free Cl to about 20 ppm (I hope).
The water, incidentally, was crystal clear prior to and during this operation. I found a small reservoir of algae hiding in a skimmer flap. Between the flap and the float chamber was a layer of black algae, this was cleaned and disinfected.
I then vacuumed the pool to waste. I put 4 Cl tablets into the floating dispenser and fully opened the water vents for maximum dispersal.
I am now running the pool pump for 24 hours continuously.
Tomorrow I will check for algae growth and probably vacuum to waste again.”

This did get rid of the black algae, but it is very difficult to eradicate. Eventually the installation of a salt water chlorination system kept it from forming again. I hope this is helpful to anyone battling black algae which normally tries to take root in the grout of tiled pools. Fibre glass pools are not usually so badly affected.

Page reviewed 31 August 2017

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