Help Plant in trouble

The plant is 12/12 from seed doing really great but in the past 3 days it has been going down hill.It started with the lower leaves having brown spots on them not like light burn but brown spots now as new leaves grow they are turning brown and shriveling up.im using cfls and mg potting soil(i no not the best) so how should i dont have the ability to order anything online so is there something i can buy from walmart, home depot and garden store??????

They are probably hungry. How long have they been in that soil and have you fed them anything yet? Pics would help, and if you do post pics make sure you take them with the hps light off

It's most likely your MG dirt!