Help me! What nutrient deffience is this?

NEEDS HIGHER NITROGEN "AKA GROW" IN YOUR FEED

Just hit it with some nutrients made for veg stage. Fox farm grow big is cheep start with 10ml per gallon every other time you water up it to 15 when plant is larger you can go as high as 20ml per gallon if plant requires. When the leaves start to get to a nice deep green then you know you don’t need to get increasing the dose

Most likely Mg, but zinc and a few others can cause this discoloration. Also if its available in the medium but the PH is off then its a lockout mimicking a deficiency. https://420life.com/wp-content/uploads/2021/10/Marijuana-Leaf-Deficiency-Chart-scaled.jpg This chart is helping in self help stuff like this.

99% of notes in a plant's life are the 6 macros, 1% is everything else as micronutrients. Until flower period there is little need for much other than the 6 macros. 4 are mobile within the plant and 2 are immobile. Immobile are sulfur and Calcium. Calcium is easily distinguishable. NPK&Mg are all mobile, leaving only sulphur or calcium. Phosphorus issues do not typically cause leaves to turn yellow. Regardless it's mobile meaning symptoms present in old growth. Your plant is primarily new growth effected. Looks like nitrogen but if it was she would present older growth first as it's mobile within the plant. Looks like sulfur to me, sulfur is immobile and only one of the 6 macros that fit. Best of luck.

Nitrogen or the begining of a phosphorus deficiency. the yellowing between the veins is a sign of phosphorus deficiency. but it could also be a ph issue thats causing it all rather than lack of something.