Doubtful it's the Miracle Grow soil, as I have never had a problem with using it for seedlings. Clones can be tricky, but it isn't the big bad no-no everyone makes it out to be.

Filling-out the troubleshooting form in my signature will help us better understand their enviornment.

You didn't feed them anything other than water at the proper ph, did you? If so, flush well with properly ph'd water, and don't feed anything for about 3 to 4 weeks. Resume watering schedule once soil has dried-out a tad. Once you start feeding, do so at half-strength and gradually increase as they acclimate.