Help with my plants!!

Ok i germed both of these plants together, The one on the left was a bigger seed but it germd slow and till now still growing very slowly the leaves ae alot darke green even tho they r the same strain Afghan Kush from world of seeds. the other plant was a very small seed it germed first with a 1/2 in tap root. and is growing alt faster than the other, leaves are not as dark as other but it is groing pretty well. any advice on the plant thats growing slow? it has not done much in 2 days. I recently upgraded to 400w mh for veg and have a hps for flower abou 6 days ago. thats when the plant really sprung into action. Also when should I start LST?Now?

I wouldnt start LST untill you know your plants are gonna start growing again. If they were growing at a good pace then I would have told you that you could have started LST within the next week.

Ok know to solve your growth speed issue. What kind of soil are you using?? Do you have both plants in the same pot??

how old are they? how far is your light? You want it as close as possible without the heat burning the plants. Take the back of your hand and hold it where the plants top are are going to be. If after 30-60 seconds your hand is not uncomfortabley warm your good, if not increase the distance between them a bit and try again, repeat that till you find where it is.