post some info on your grow if your looking for help....ph, soil/hydro, temps, humidity, how often your watering, how often your feeding, how far into flower, strain, ect. just by looking at the pics, I would say nutrient lock out due to over fertilizing
I thought it looked like nutrient burn which you may have recently increased nutrients per feed etc ? that alone may suggest the dark green leafs which may well be nitrogen abundance pushing border line toxicity problem...
That is just an assumption made purely from the pic's & some instinct by the way !
Might be wrong in till further detail is applied by the OP
all in all she looks great except for that little bit of leaf burn.
help us out with a few answers
What Strain is it?
Is it Indica, Sativa or Hybrid? What percentages?
How Many Plants?
Is it in Vegetative or Flowering Stage?
If in Vegetative Stage... How Long?
If in Flowering Stage... How Long?
Indoor or Outdoor?
Soil or Hydro?
If Hydro, Reservoir size?
If Hydro, Reservoir Temperature?
If Hydro, what type of Medium?
If Hydro, what type of Setup?
If Soil... What is in your Mix?
If Soil... What Size Pot?
Size (Wattage) of Light? How Many?
Is it Air Cooled?
Temperature of Room/Cabinet?
RH of Room/Cabinet?
PH of Medium or Reservoir?
How Often are you Watering?
Type and Strength of Fertilizers used?
Size or Square Footage of Room?
This information is necessary for accurate support to be given.