Stalk very thin and tall, what's going on?

Hi folks, ok so started this plant from seedling just over a month ago 2/13. Took almost a week to germinate. From there it went into (presoaked) rockwool for a week, on 2/28 into an Emily's Garden with a mild GH seedling solution. On 3/6 transferred into my hydro flood/drain system with a "week 2 early grow solution". On 3/12 changed to "week 3 late grow solution". Now, with all that said. There is 1 other plants that was started at same time (and one a week later) that is/are doing much better. The strain in question is a Northern Lights Blue. Any input is greatly appreciated. 1st pic is sick little girl, 2nd pic is sick one and 2nd one started at same time. 3rd is all 3 with one on right being a week younger and healthier than 1st 2....

are they all different strains? I did a cycle with 4 different strains being fed from the same reservoir... 2 of the 4 strains ended up like $hit, the other 2, wicked dank. I guess my point is that different strains perform differently... even under the same circumstances

Yes, each one is different. As you can kind of see there are others in the system as well. They are older plants (4 different strains) and all doing well.