seedlings have yellow spots on them

this is my first try at growing, and I have a 8 seedlings that have sprouted. they have been sprouted for about 10 days. i have one that started out the strongest, but it is showing signs of a yellow spot on one of the cotyeldons. I started out with just using distilled water with rockwool cubes. i made sure to dip the rockwool in a lower pH solution and they germinated fine. after they sprouted, I inserted the small rockwool cube into a larger one and started on a 50% nutrient solution and fed them 3 times a day through a drip-irrigation system for 2 minutes/feeding. I also am using high output fluorescent lights that are about 4" above the seedlings. I am trying to make sure not to over water and have been checking the cubes every 8 hours to make sure they are not over saturated. i have the temp around 68-70 and have added a warm air humidifier to keep the humidity around 30-40%. I have been referencing some very good books, however, none of them talk much about the seedling, most of it is about the very initial stages of seedling, then jumps right to veg growth. anyone know what that yellow spot is? The pH is 5.8 in my solution, and the PPM is around 400. please help! thanks!

your nukeing it no nutes until 3 or 4 leaf sets try water ing straight water for a few and see if it helps

This is really annoying.

Your seedling is dead. Next time, no nutrient solutions until 2-4 weeks old.
If you want it to grow fast, use better lights. Don't pump it with lots of nutrients.

ok, thanks! i'll try again. live and learn!

since your still new if i were you and i was before go get some fox farms ocean forest soil and use that all you need is water for the first month and some people go whole grow with out add nutes but if you use nutes never use more than 2/3 the doseage it says and you will rarely end up having any problems . LESS IS MORE if you need any help pm me and ill help with whatever i can check out my journal in my signature

You can actually get a lot of seedling care information online.

Good luck on your future endeavors