Bagseed Kush (first grow ever)

Your PH should be between 6.2 to 6.5, from seedlings to harvest ! Your non-adjusted tap water may have affected your plants. But more than a PH related problem, this looks like a nitrogen deficiency. I also use Biobizz nutrients and never experiment a deficiency like that but I would recommend you to use "BioHeaven" which should increase nutrients absorption and globally enhance plant energy. The dosage is 1.5 ml per liter of water, starting at the second week of growth and ending at least 2 weeks before the harvest. You could also try to add a very small amount of BioGrow, something like 0.5ml/L if your harvest is not planned for the next 3-4 weeks. Finally, a couple of questions to better understand your situation : how often do you give them nutrients? And how often do you give them plain PHd water ? How many liters do you give to each plant and at what frequency? I'll be around, good luck with this beauty!