Deficiency ?

I disagree. With N you'd actually see an ongoing issue. This is a plant that's fed on itself. That's all. Soil moisture is key. If it was a N issue. You'd see 1 leaf really yellow. This is signs she draw fluid from that node as it was the closest source of food at the beginning of the stem.

I agree with Stormyluca, that plant is hungry for some nutrients. Biobizz seems to be low on everything after 4 weeks, thats what i heard from people around me aswell.

Hey, This is a Nitrogen deficiency. I am really not a fan of biobizz because a lot of beginners have problems with it. I can recommend chicken manure pellets and organic fertilizer in general