You shouldn't be fertilizing it with anything right now; baby plants have enough energy within themselves to grow to about 3" tall or for the first 2 weeks. 1/4 strength is plenty after that for another couple of weeks. Looks like it might be overwatered also.
You can grow in rock wool or soil if you're not doing hydro. Ferts (nutes) is what we add to give the plants the nutritional needs they have; the soil is just the medium.
looking at the pics - what sort of soil you using - had probs with mine but changed to proper grow stuff and they seem to be recovering - i was just using cheap compost from the market, never again
well i bought both from homedepot 1 of them is organic and its supersoil brand the other is miracle grow i know its not good but im changing to that foxfarm brand if i could find it
