It's Purple Kush and 9 weeks of flowering....and I'm on week 7 of flowering
My thinking, without more details (grow medium, pH of medium, current details on feed mix, TDS, EC).... follows this:
Dark green leaves (likely too much nutrient, or improper mix)
Leaf tip burns turning into burned up leaves (likely too much nutrient)
The buds look good, as do the plants, generally.
If you skip a week of feeding and just give pure pH adjusted water, you're in week 8, and week 9 you'd be using just water too.... but that is a soil medium pov.
If you're in a hydro medum, you'll need to provide all the details about your hydro solution's current state.