Seeming some issues

It's a simple ph lock out. Likely from feed too strong or not enough run off during feeding. Which has created a salt build up that spiked your ph down.

It looks like either phosphorus or potassium, I get them mixed up. Also the plant does look like she's been over fed. Let your soil dry up a good inch at the top before next watering, you possibly will have an abundance of nutrition in the soil, so just water at PH6.3-6.5, take your time and let the water soak in, get yourself a decent amount of runoff and capture the last bit of runoff and test that, hopefully your ph will start to rise. Your then looking for new growth to look good and the damaged growth not getting worse.

Looking at diary its toxicity, that led to lockout and now all troubles starts. Reminds Phosphorus deficiency by leaf downgrade. If no tips would stay healthy after necrosis - would say potassium, but here i see some bits left healthy . Your plants looked very droopy sometimes, maybe you don't have wet/dry cycle ... its a must in soil grows.

Hi also ich würde schon den ph wert zwischen 6 und 6.5 halten, je später in der Blüte desde näher an die 6.5. Canabis braucht in seinen verschiedenen Phasen ein unterschiedlichen PH wert da sie verschiedene Nährstoffe aufnehmen muss und diese mit dem PH wert verbunden sind. Lange Rede kurzer Sinn Pass den ph wert. Es sieht so aus als könnte dadurch eine Blockade entstanden sein und die Aufnahmen von CalMag und Phosphor beeinträchtigt worden. Wenn du jetzt gegensteuerst wirds wieder, aber die Blätter die beschädigt sind werden nicht mehr gut, die neuen sollte aber wieder normal kommen sonnst stimmt das Verhältnis immer noch nicht. Viel erfolg

It's lower because your plant is taking the nutes out of the water to give a higher pH water is not correct nor will it help. You want to give same pH to the root zone time and time again so they don't need to keep adjusting to absorb what she needs. Hope this helps.peace and love.