FLOUROS DO PUT OFF ENOUGH HEAT TO KILL SEEDLINGS. YOU MUST HAVE AIR FLOWING FREELY BETWEEN THE LIGHT AND PLANTS. I HAVE SEEN CLONES/SEEDLINGS KILLED MANY TIMES BY NOT ENOUGH AIR WITH THE LIGHTS ONLY 2-4INCHES AWAY. sorry about the caps, i didn't notice the caps lock was on till i was finished typing. it is hard to overwater seedlings, alls you have to do is not let the soil dry out for the 1st few days. my money is on heat as the killer, you still haven't posted the temps or what kind of ventillation. without any info all the answers are just guesses.