Seedlings that show these symptoms are already goners. I suggest you sprout the rest using the ziploc method. Wrap the seeds in moist paper towels (not wet!), put the whole thing in a ziploc bag or anything similar that would seal in the moisture, and put the bag on a heat mat or somewhere warm. After 1 week, check every 2-3 days so as to catch the seeds when they just start to pop open and sow them or else the roots will curl up and it will be a crap shoot when you sow.
And when you sow the seeds, keep the soil moist but not wet and NO fertilizer until you get at least to the 2nd/3rd flush of leaves. These steps work well for me.