I actually used miracle grow a while back and had the exact same things happen that you're experiencing. I pretty much let them do their own thing, and when the soil got dry enough, I flushed the crap out of them, and let them dry out and repeated. However my seedlings have all come back so far and are starting to take off better.
You can see this one had yellowish leaves at first as well as a bit of burning on the tips but the new leaves are darker, and look healthier that the first set.
A buddy of mine from a nearby dispensary gave my this giant bubba kush plant. He started from seed, germinated and grew this girl in a 5 gallon pot of FFOF soil ph is 6.5 and she hasn't been fed any nutes at all, Only RO water.
Obviously from now on I will be using Fox Farms. lol
(sorry about posting the pic, if you want I can take it down.)