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, I would keep the pH value between 6 and 6.5, getting closer to 6.5 the later you are in flowering. Cannabis needs different pH values in its various phases because it has to absorb different nutrients, which are connected to the pH value. Long story short, adjust the pH value. It looks like a blockage might have occurred, affecting the absorption of CalMag and phosphorus. If you counteract it now, it will get better, but the damaged leaves won't recover; the new ones should come back to normal, otherwise the ratio still won't be right. Good luck!

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.