Actually, you can kill it. Monochloramine* (chlorine + ammonia + high-ish pH) will kill it. But it's such nasty stuff . . . and pools prone to algae tend to have it come back even when you do kill it.

Copper will also kill it. But then you get stains and green hair. (I've actually DELIBERATELY stained pools that had very rough porous plaster.)

Super high chlorine will kill it.

But . . . it appears that moderate levels of chlorine will kill it when phosphate levels are very low. So that's what I'm experimenting with, now.


* Products like Yellow Out and Mustard Master work this way.