Before you know what your nutrient program looks like, what water you're using, and what your pH is, I wouldn't rely on standard answers. It could just as easily be due to overwatering, which might not even be directly your fault. My buddy had similar issues with Compo soil, which tends to stay too wet and doesn't have as good drainage as Canna, Plagron, or Biobizz. And Compo isn't very pH stable. Go through the process of elimination.
1. Check if you're watering correctly
2. Check the pH
Review your nutrient program and your water.
Is your VPD in range?
Too many unknowns for a good answer, buddy. I mean well and don't want to give you bad advice.
3. Provide as much information as possible in your next question so that more reliable tips can be given that really help.