Mustard Algae and Poly...How Much and Other Q's

Have mustard algae in 22,500g IG, gunite and plaster pool. San Diego Co. Autopilot SWG, no fancy water features. 7 ft. attached spa.

I raised ch levels to 15ppm. After keeping ch level at or about 15 for a number of days, I held off on adding more chlorine yesterday, and the mustard returned. I was brushing at least once a day, ph was good (7.4-7.6). oh well. Ch is still registering about 12/13ppm (I don't have the most accurate method of testing...yet...just bought Ben's kit).

Figure it is time for poly. bought some poly today, the 60% strength. back of container says 11-17 oz per 10k of pool. I have 22,500g in ground, gunite and plaster. So that's 25-38 oz (container is 32 oz). Should I just put whole thing in there? Any problem with adding poly with pool with ch levels in low teens?

Thanks for the help. I'll cut and paste this over to the algae forum.