so you're saying you used full-blown compost soil for them?
then it might be over nute, compost can be too hot for young plants. but you said it was a mix so i thought maybe it was adjusted.
so it's really hard to tell, if this is too much, too little or not even about nutes but about pH. one thing is clear - the current way of work is not working. so I suggest you change as much as you can of it, and odds are that your problem will go away (might be replaced by another problem though). try to mix your soil with a light soil if you can find it. if not, maybe 20% perlite/vermiculite/soilless mix. that will eliminate the possibility of the soil being too hot.
also make sure you water @ pH 6.5 +-
and give them a flush. adding nutes should be your last resort and only after flushing. better to use organic nutes and don't put too much in.
whether taking these steps will solve it or not, aerated compost tea is always a good idea (dilute it at first if you fear of overnute). it gives harmony to your soil, as well as nutrients.