Is this black algae

[poolcurious7]

Hello. I just noticed this tiny black spot in my spa.
I haven’t seen any other spots anywhere else.
is this black algae? Thanks!

 

[ajw22]

Probably not....

Gently scrape a sample of the suspected black algae with your fingernail and then smudge it on plain white paper. If the smudge scrapes off and is a greenish color, then it’s black algae.

Black Algae

This guide provides a step by step procedure for eliminating black algae in your concrete or gunite pool. Read full post here.

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[Donldson]

Could be, but is there any chance that a pellet of lawn fertilizer might have gotten in to the pool?

 

[poolcurious7]

I brushed it a ton so
Will the fingernail trick still work?

could be lawn fertilizer. But not brown/orange

 

[JamesW]

Try to scrape it.

If nothing comes up, put a vitamin C tab on it.

 

[poolcurious7]

Scrape with what? My nail? Is a pebble surface. It seems to be more in the crevices after intense brushing

 

[JamesW]

Put a vitamin C tab on it.

 

[poolcurious7]

Thanks. We had a terrible storm here and a ton of landscape debris blew in my pool and that spot is where a dark leaf was. Wonder if it’s related?

 

[JamesW]

Put a vitamin C tab on it.