Seedlings foliage turning yellow

[Sandy Zone 3b]

I noticed on some of the new seedlings the foliage is turning a pale yellow, I fertilize with 10-52-10 plant starter fertilizer at a weak solution.
Even after transplanting them into 6 paks and potting soil the leaves look limp.

[Sharon Bryson]

Hi Sandy:
I can only speculate as to what the problem might be.....too wet soil being one. If your potting soil is a bit too dense, it doesn't dry out fast enough, and oxygen levels can be low.
You could back off on the 10-52-10.....seedlings need very little fertilizer.
Are temperatures moderate, as opposed to being really warm or really cool?
Sorry for more questions than answers!

[Sandy Zone 3b]

The temperature have been constant all the time.
I'm beginning to suspect the planting mixture, it's not like the first bag I used. I did add some perlite and peat into the mix. and tried to keep from watering too much. Most of the ones that are showing these problems are still under the lights.
When I started the seeds I used a mix especially for seedlings, and only slightly dampened them.
Now as they're growing I wondered how much water to give them!