Your plants are too scrawny. There is too much internode distance, the distance between one set of leaves
and the next. Two immediate reasons come to mind.
First, genetics. Are your plants from bagseed? If the mother plant was scrawny the kids will be scrawny too.
Second, they are not getting enough light. If 400W. is all you can provide, at least put the light right above the plants.
Use the hand trick -- if you place your hand on top of the plant and can feel the heat of the light you are too close. So
get the light closer to the plants.
If you are not in a particular hurry and want your plants to yield more I would top them. Chop off the top couple of nodes
where there is so much distance between leaves and use a good all-purpose vegging nute. I use MiracleGro's 24-8-16 for
vegging. When they get to 26-30 inches turn the light to a 12/12 schedule for flowering. I use Liquid Bloom's 3-12-6 for
flowering.
Good luck, BigSteve.