Seedling Issue

[heyni1]

Hello,

I started a few flats from seed about three weeks ago. Everything germinated great so I removed the domes and put them right under the lights. Set up seen below.

The two flats on the bottom never developed their first set of true leaves. The cotyledons turned brown and sick looking. I suspected maybe the bottom trays were either not getting enough light (new weird pink grow lights which may stink) or it was colder on the bottom.

I moved the two problems flats up and covered them in the domes again. They seem to have bounced back after a few days covered and now have healthy looking true leaves. The cotyledons are dead looking. See plants below.

My questions are should I trash the whole flats since they may be diseased and would lack of light temperature cause those symptoms?

Thanks.
nick