Help please

I am a firs time grower, doing 1 kings kush and 3 g-bomb, they are under a 600w hps they are two weeks old and 2 of my plants are quite tall whilst the other 2 are lacking in size. they are all looking quite healthy but they have really light green leaves with yellow running through this. What could be wrong with them and how can i prevent this from destroying my grow.

sounds like Nitrogen def. give it some food .

^^what he said

nitrogen def. just pump in sum veg nutes at 1/2 str
they are only 2 weeks old so be careful with your nutes