Simpler:

When everything is fine, no algae is present, and the bather load is light, FC = 5% of CYA (0.05 x CYA ppm = FC ppm target).

Under heavier load, 10%

With green algae, 15% - 20% or -- long term -- to remove black algae.

Mustard algae, 25% - 50%

With borates > 60 ppm, and especially, with phosphates < 125 ppb (0.125 ppm), the algae treatment levels can be lowered.