Deficiency or pot too small ?

Maybe needs N.. i don't see a P deficiency... And possibly K-deficient. But if that yellowing occured tip-in on leaves and from bottom up on plant, then formed necrotic tips... i'd stick with N. But yo need to first ensure pH is okay and that it is not rootbound. these are three different molecules needed in 3 different concentration relative to each other. low on "npk" is not a a resolved answer for this. It's basically just saying add fertilizer without a concern for the which component is actually off or if it was caused by rootbound and being fed just fine. following this blindly would likely result in compounding current problems with new ones. Make sure it isn't rootbound (roots wrapping around multiple times is a good clue), cause that would need to be cleared up before reacting to any visible symptom on the plant. Pot size will definitely starts to come into play when canopy is larger than a smaller pot early on. What used to keep it happy and healthy may not anymore even with an optimally balanced mix. A better mix will keep it happier for longer, but will eventually fail in this context. (with a larger pot, there's a bit more leeway as you go up.. figure 1gallon per month in the pot is safe. So, a 4mo grow should be at least 4 gallons.. this is just a generalization) Another good sign it is rootbound is if the vertical height has stopped or slowed significantly. It will get rootbound at some point and it'll choke itself and cause oddities in leaves even if there is plenty of "npk" and don't forget about "Ca/Mg/S" as those are equially important as NPK.

Hi! For sure the pot is small (not "too" small but you have to change it) and she has a npk deficiency (Yellow leaves-red stems-burned leaves) :) Happy growing! Remember to check ppm and ec!