Seedling with pale green first leaves

I have ten seedlings and two have pale green first leaves while the others are dark and healthier looking. They are in identical conditions in DWC. The only other observation I can make is that they seem to be slower in getting the second set of real leaves than they were the first set. I've been waiting for that to start light nutes. They have been under a 90w led ufo, but this am I put a 250w MH about three feet over them thinking maybe they need more light.

Thoughts on the pale green are welcome!

You ought to post a pic you will get more responders~
Your always have some that do better and some that
do worse or slower seedlings. This is why I always
start a few more than need. Try to veg one or two
extra so I get four nice plants to flower. I only have
root for 4~ But you veg more in less room!

is it perhaps too dry in your grow room? is your PH optimal? and dont ever feed your seedlings until the cotelydons fall off