seedlings- curling leaves?

i got some seedlings and they are about a week-10 days old they are in rockwool cubes and i had them under cfls but just put them under my 600 watt mh light. the first set of leaves to come in (not the round ones) are starting to curl down since it cant be from nutes since i am not using any yet do you think it is from over watering? i been watering the 1 in rockwool cubes about every other day but if i noticed the rockwool seemed really dry on top i would give it just a little water in between there regular watering. is this prob a over/underwatering issue or a light issue?

keep them under cfls until there a month old.

if you can, keep them under CFL's as well as introducing the 600w, gradually bring the light closer to the plants day by day until you are about 15 IN. away. leaves curling downward is usually a good indicator of over-watering stress, but, BE WARY, the only person who could really tell you is yourself, go with your gut feeling,the last thing you wanna do is starve seedlings of nutrients and water. With enough TLC and some common sense you should have no problems.good luck mate