fighting mustard algae

[Kateyru]

pH = 8 was before I started shocking...which I'm doing now. I'll add acid to lower pH now.
I'm such a "rule-follower" that I try very hard to do exactly the right number...glad to know it's not that exact. How long do I maintain mustard algae shock level?
Final, for now, question...previously you said that I could either keep FC at 15% of CYA, use polyquat 60 weekly or use phosphorus cleaner weekly re: mustard algae (and possibility/likelihood of not getting rid of all of it since I couldn't remove my light and clean the niche). Will any of those options actually get rid of the mustard algae or just keep it out of sight?
Thanks so much!!!

a few minutes later...
Hmmmmm...I just tested FC. This am at 7, FC = 41.5. I had to be away most of the day so turned SWG on at 50%. Just tested at 4:15 pm, and FC = 23.5. Quite a drop, considering SWG was running. So, do I start all over re: shocking? Just added acid to lower pH. How long before I add bleach?