What is happening to the leaves?

Hey man, that one is a perfect showcase for a nitrogen deficiency. The reason the plant in soil is doing great while the others arent't is because the soil is prefertilized with basic nutrients that probably feeds the plant for a few weeks from the start. In coco however there are no nutrients at all, NONE. You definitely have to feed the plants sitting in coco fertilizer that contains some Nitrogen.Depending how old they are, be careful not to add too much to the soil plant yet, there are probably still nutes in the soil, so go slow! Would be great to know if you use synthetic nutes or organic. Either way, make sure not to add too much just because they need it. Add small amounts (50% or less of supplier recommendations) and work your way up or down from there. The deficiencies are easy to handle, but once you feed too much you'll have a lot of problems. Hope I could help, cheers my man and good luck, the plants look great anyway!