I have seen that before but what is weird about your plants is it is happening to all the leaves except the Cotyledons (Seed leaves).

For anyone to try to diagnose the problem, you should provide more information like, temps they are in, amount of light, type of soil, nutrients added, amount of water, etc.... Oh and what variety of pepper are they?

They are colossus bell peppers and anaheim. They're grown in a heated greenhouse maintained around 65F, with CFL grow lights on for 14 hours + natural daylight. It was pretty cold until last week, 50 degrees daytime. This week suddenly turned 70 degrees daytime with intense sunlight. They're still in a standard seed starting blend from sungro since they were planted a month and a half ago, but we've been adding some epsom salt and miracle gro to the water since 2 and half weeks ago. They are watered once a day. I thought the leaf curl may be from the intense heat and light recently, but I have no idea why the leaf is shaped like that as that seems to be how it was grown and not sudden environmental stressors.

I would hold off the nutrients. I am sure the seed mix had some built in ferts. Stop with the epsom salts and MG for a while and see it that doesn't help. Also, don't water them until they need watering.

It is hard to see what size containers your guys are in. Are they in those 1" or 2" seed starting trays? If so, for petes sake, repot those little fellas into some bigger containers.

They're 1" squares. I wish I could repot, but we have 50 trays of 200 plants each filling up that greenhouse. Thats why we add fertilizer since they probably already used a significant portion. They're due for planting in a couple weeks anyways. If it might be a excrssive nutrient problem, it should be okay for now. I'm just worried it might be a disease or something that would cause dieoffs. Thanks for your advice!

Well, yah, I would hold off on the ferts. With that little soil, you could easily be over doing it. But, the cramped space is probably more of a source for the problem than anything. If you can't do anything about it now, I guess you will just have to deal with it, but that is clearly not an ideal situation you have going on there.