You just over watered them. If the leaves are curling but still moist i.e not dry and crispy most probably you just overwatering. Only water them when they need it i.e. when the soil it wet. Also tin foil is no good as it creates hot spots on your plants. Matt white surfaces are the best reflective surface so ditch the tin foil.

Also if you put them into MG soil i doubt you will need to give them nutrients for a little white 3 weeks probably.

Good luck