After water + applying fertilisers BioBizz flowering week 4 (see chart) the leaves turned dark and in a few hrs started yellowing. The runoff EC usually is a little lower than solution EC. pH around 6,25-6,5
Might be that your girl has used all the goodstuff in your substrare and needs a re charge. This has happened to me before. The biobizz organic feeds work in tandem with the soil. If the soil is depleted your girl will show signs of deficiencies. I up potted mine to 5 gall pots with fresh substrate as I still had around 6 weeks of flowering till harvest. After which I continued to add nutes in water as per schedule. This corrected most deficiencies after a week or so. Previously effected leaves will still show deficiencies but new growth will appear healthy. Other than that you have a good grow going. Best of luck man.