you answered your question in your post my friend....

the curling is from the miracle grow. over nuting will result in curled tips, yellowing tips.

you should NOT be nuting AT ALL throughout the stage your in. NO nutes for the first 2 weeks...seedling have enough energy from their seed, and there is enough trace nutes in brand new soil (even if its soiless) to feed them for 2 weeks. After that time you can start to nute....you start out with 1/4 or less of the full dose....and you work your way up SLOWWWWWWLY. Keep close watch and learn how your plant reacts to nutes...every strain is different...some need more some less. if you start to see nute burn, back off....if not try adding a hair more at a time. I also would not recommend anything miracle grow. but you go that route your next grow....search the boards here and learn about the liquid nutes people use.

my suggestion to you is, back off the nutes, give your plants a moderate flush since youv'e probably over nuted them. and go about the nutes the way i described. also moderate the PH of your soil always...if it falls out of range you plants wont use the nutes