5.9 in soil is too low, somewhere arond 6.4 would be better.
Yes, food.... at this stage of flowering, they will need a "bloom" type of fertilerzer, not a "grow" as your diary shows.
Basically, she is hungry for potassium and phosphorous.
Sieht aus als könnte die Pflanze kein Kalziums und Magnesium aufnehmen aufgrund falschem ph wert im Boden. Habe das selbe Problem grade. Der PH wert sollte so zwischen 6,3 und 6,8 liegen.
Looks like a potassium deficiency by the discoloration and spotting. Flowering npk ratio is 1-2-3. That , or if you are growing in coco then it could also be ph issue in coco.