Help, please. I have been lucky enough to never have an algae problem til now: got that yellow "sand" which seems to brush off but reappears 8-24 hours later (on walls and where walls meet floor, etc. (IG 18000 gal, FC 2.0, Ph 7.6, Total Alk 80, CYA 50, Temp 86).

I've been told this is likely mustard algae/pollen. Unfortunately, I sent someone else to the local Leslie's (in a panic) and they prescribed:
a) bring PH up to 8.0
b) Add Yellow Out + shock (they said my unstablizied chlorine (e.g., Sustain brand CalHypoChlorite would be fine)
c) Wait a day, or two, vacuum and backwash and then restabilize PH (either let it drift over time or Muriatic acid)

This sounded OK until I read the bottle of Yellow Out and it says it is NOT an algaecide. Did we get sold a (wrong) package of goods here?

Thanks.
-Marty