1) is there a way/procedure to use fewer drops of R-0871 when repeatedly testing FC at mustard algae shock levels?
You can use a 5ml sample and multiply drop count by 1ppm. If you have a way to measure 5ml.


2) should I continue to lower TA (by adding acid to lower pH then aerating then repeating)
I see no reason to move your TA.


3) When should I add CYA to raise it? I've added several times this summer and am surprised it is as low as 35 but I triple- checked it today
Whenever you want to. How do you get 35ppm? Halfway between 30ppm and 40ppm?