autoflower seedlings not looking too chippa - help needed asap

Hi all, i have recently planted 4 autoflower seeds, today will be day 11 since they were put in the coco. I had been away for 3 days and when i returned the plans had deteriorated some-what. (they had looked a bit dry when i returned, possible under-watering)
Some pictures:

The 3rd picture is a newly planted one, about day 6, looking better compared to the other 3. They have all been watered with ph corrected tap water, ~5.8pH 240ppm, tap water here is 8.1pH so takes a bit of buffereing to get it down hence the high-ish ppm.
The 4th and 5th picture show the most ill looking plant, its 2nd set of leaves are pretty much dead, yellow/brown and crispy. I thought the light may have been to close so have risen it so its a good 15" away.
Don't know whether they need some nitrogen feeding, they are turning more yellow than green or could be a result of over watering.

As i stated in the title, help as soon as possible is greatly appreciated, im a bit stumped on what to do.

Thanks, Collie

looks like over watering to me. anytime ive over watered my babies, the stem turns dark like yours are. what kind of light are you using? when their that small i would use cfls for sure and keep them very close 1-3 inches away

cheers for the response, im using a 250w mh bulb, dont have any cfls by hand, only a smaller 150w hps.