overwatering most definately. The excessive heat isn't helping your cause either. If your using MG soil nutes are realeased as you water too so it can be very troublesome if you overwater it for that reason too. I say transplant all those smaller plants into bigger pots with a good soil that drains well than water thoroughly and let the soil dry out a little between waterings. Don't want to starve your plants of water and end up with crispy seedlings like I had the other day because you were trying to not overwater and the temps are frying your soil. Especially in those peat pots they can dry out quickly and I don't want you to dry em out and kill em because I said you were overwatering. By plaving them into the bigger pots with soil the extra soil will keep everything nice and moist but you may have to add just a little bit of water to the inside of the peat cups until the roots can expand into new soil. Check my drgreenthumb journal in my sig if you want to see the sprouts that I killed in my veg box in a matter of hours with high temps and no water. Had I transplanted them I wouldn't have had that problem.