Stubborn Black Algae spots

[supersteel]

Experienced guys please suggest a solution for black algae as appears in pictures below. I have this black algae spots for about a month or so. I have tried to scrub it off but no luck.
have done SLAM two weeks ago but no luck. Below is the current water analysis.

Total CL - 1.5
Free CL - 1.3
PH - 8.1
Tot Alk - 73
Adj. Tot Alk - 52
Hardness - 230
Salt - 3200



View attachment 50907View attachment 50908

 

[BoDarville]

Welcome to TFP!

While other forms of algae are primarily removed with SLAM-level chlorine levels, the key to removing black algae is brushing - elevated chlorine levels alone will not be effective on black algae. You may have to go with a stainless steel brush on a plaster surface in order to knock off the algae’s protective coating so that the chlorine can attack the algae itself. As for chlorine the chlorine level, maintain it between the high end of the recommended “Normal” range and the Shock (SLAM) level according to your pool’s CYA level. For example, if your pool’s CYA is 40, the high end of the “Normal” FC range is 7 ppm and the Shock/SLAM level is 16 ppm. In this case, you would maintain it between 7 and 16 ppm. I do not see a CYA level in your test results. You will need to know that parameter in order to determine your targets and dose chlorine properly.

For more info, see Black Algae

 

[supersteel]

Thanks for the reply ! I will try to follow that.
Btw CYA is 70.


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