How To Use Progressive Web App aka PWA On 420 Magazine Forum
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For a question like this, it would get more views in the FAQ section, or Grower's Lounge.
This could be a multitude of problems. What kind of lighting are you using? How close are the lights? What nutrients are you using? When did you last feed nutes? What is your growing medium? How big is the pot you're growing in? What is the PH of your growing medium? Did you replant them recently? Did you dig in the growing medium at all recently?
My first guesses would be, in no particular order:
Too much water
Not enough water
General Stress
Nutrient burn coming on
Heat stress