I wonder why these leaves are yellow. Ive got it under a 400w HPS light, organic seelding starter mix. it's about 80 degrees (ugh) and a 40% humidity. The other plants are fine, even thriving. I'm using purified water I bought from the grocery. I don't really have a watering schedule, if it's dry I water it. This is being grown in a closet, I also included a pic of the setup.
Seedlings will shrivel up and die if they under that hot of a light. Get them out of that light and put them under a couple CFLs for a week or two. That should fix your problem.
And, it sounds like you're watering it right. An easy way to check is stick your finger in the dirt 2 or 3 inches down, and if its dry, water it. If it's still moist, don't.