I'm concerned with the really purple stems, the yellowing of the fan leaves, the burning on the margins ...
How are the fan leaves at the bottom of the plant?
You don't pH because you are in organic soil?
The fix could be as easy as flushing or up-potting.
Anyway, I think we have a bunch of info now - but the type of info really helps us to diagnose a lot easier:
Pictures
Pictures should be taken under white light - Blurple is too difficult to diagnose.
Pictures should be clear and not blurred.
Please provide a group pic of your plants.
Please provide a top to bottom pic of your plant.
Please provide a close up of fan leaves with issues.
Plants
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?
Location
Indoor?Outdoor?Green house?
Grow Room
Room? Closet? Tent
Dimensions - Length x Width x Height?
Is is light proof? Pitch black?
Grow Environment
Is it Air Conditioned?
Temperature of Room/Cabinet?
Is there a humidifier/dehumidifier?
RH of Room/Cabinet?
Air
Fans for exhaust?
Fans for air circulation?
Are you adding CO2?
Grow Lights
HID or LED?
Size (Wattage) of Light? How Many?
How far above the canopy are the lights?
What is your schedule? 20-4? 18-6?
Sunlight
How many daylight hours currently?
Grow Medium
Soil/Coco/Peat or Hydro?
If Hydro, Reservoir size?
If Hydro, Reservoir Temperature?
If Hydro, what type of Medium?
If Hydro, what type of Setup?
If Soil/Coco/Peat... What is in your Mix?
Containers
If Soil/Coco/Peat... What Size Pot?
If Soil/Coco/Peat... Fabric or plastic?
If Soil/Coco/Peat... When was the last time you up-potted your plants?
Water
pH of Medium or Reservoir?
TDS of Medium or Reservoir?
How Often are you Watering? Feeding?
Do you flush your plants regularly to remove salts and debris?
Nutrients
Type and Strength of Fertilizers used?
Are you following the nutrient line's feeding schedule?
Pests
Any Pests?
Have you used a jewelers loupe to check for bugs and bug larvae?