"Mustard algae tends to grow on the walls and floor of the pool on the shaded side."

"Another way to distinguish between the two is that when you go up to shock level and brush the pool, mustard algae won’t come back as long as you stay at shock level."

From the article. Color is not a definitive marker.

Your post was moved as it was either to an old thread or a hijack. I do not remember which.
 
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