The vast majority of the time, the "cloud" is:
a. dirt
b. pollen
c. dead algae
They can all look/behave similarly.
c. can be dark brown, medium brown or brownish yellow. No way to tell from the look what kind of dead it is.
If it has a greenish tinge, unknown if there is still living among the dead - but it is pretty highly suspect.
Live algae tends to be a bit sticky, so you have to lean into the brush a bit to get it off. And tends to make greenish clouds.
Yellow algae is a thing, but less likely than most think. It's hallmark is being very resistant to chlorine.
Do a full SLAM, making 1000% sure you pass
all the criteria, including cleaning all nooks and crannies. If you then lower CL to the recommended range (but never to minimum) and it comes back quickly (a few number of days), then you might have mustard. Or do the regular SLAM again. And if it then comes back quickly again.....
Pool Math said both, in "Effects of Adding".
@Newdude beat me to it while I was typing the other!