Which deficiency is that?

Please help me understand which deficiency is that, this is jack herer in 4th week, thanks.

I'm not really seeing any deficiencies. One leaf tip showing an issue isn't something to necessarily cause alarm. Is this prevalent throughout the plant?

Perhaps ph, toxicity, fan blowing right in it, watering during lights on, a need to up pot...

It honestly could be a number of things. May you provide us with a little more information?
Your watering system, soil composition, fertilizing plan, pot size, do you ph water, etc...?

The roots seem to have reached the bottom of the pot. Some plants do react more to this than others. Soon time to repot, but not yet.