After a successful start, I am having issues with my tomato seedlings. Here are the details:

-Starting mix- 1 part vermiculite, 2 parts compost, 3 parts burpee seed starter (coco coir)

-Some planted in 2"x2" fiber squares, others in 3.5" round fiber pots

-Water when soil is dry and grow light 14-16 hours a day

Here is the strange part. The ones in the 2x2" squares stopped growing, while the ones in larger pots surpassed them. Now they have all stopped growing it seems. Any ideas why the ones in the smaller planters stopped growing so soon?

They have some whitish brownish stuff on some of the leaves. This showed up after I thought it might help to get them out in some sun. I am starting to see that might have been a no no.

What should I do now? Do they need some fertilizer? Have they had too much water, not enough? I will describe what you are seeing in the photos. Any help is much appreciated.