puzzled

Ok im new to tis site but will be on frequently. now this is my 5th grow so still kinda of a newbie but i have done alot of research and had my last 2 grows have been very sucsessful. now i have 2 seeds from bag that are big bud x og kush. they have had a little ph burn but are now good. But here is my question, the ones on the sides are the BB and i have a clone i just put in there which is exodus cheese. the one one the right is the one i have the problem with. its growing a little slower and i have no idea why it looks like it is toped already can somone please help.

Whats the nutrient mix?

Some require less nutrients then some, So using one nutrient mix for all three diffrent strains might not be the best setup.
So that one that is falling behind can be suffering from over fert, while its good for the other two but this one might need less then the others.

im sorry i wasent clear on my question. the plant i have from seed is growing 2 sets of leaves instead of one. so i was wondering if this is a good thing or a bad thing?? i know when it gets bigger there will be issues with the weight but i would like to know if this is a good trait or bad basically.