My bad.

CYA = 50 ppm; mustard algae level for FC is between 15 and 30 ppm.

+ Add a first dose of 6 gallons of plain 6% bleach.
+ Make sure NOTHING is in the skimmer (no dirt, no chemicals) and pour the bleach in via the skimmer while the pump is running.
+ The following evening, add enough chlorine to raise the level to 25+; then brush the pool completely, then add another gallon of bleach.
+ Hold the chlorine level between 15 - 30 ppm for 1 week after all traces of mustard algae are gone