Seedlings getting yellow leaves that turn necrotic and become brittle...

Week old seedlings,mix of Hashberry.Skunk master and Master Kush....seedlings all sprouted great,put into organic soil mixed with vermiculite , peat moss and vermiculite. PH is 7 water used to irrigate is 7,temps a constant 78 degrees with about 50% humidity took off great and suddenly getting yellow spots that become necrotic and brittle . Containers are allowed to dry before watering,I am using 32 oz. cups to grow in before transplant......pics are not available right now so I know it is hard to diagnose without them,but was just wondering if anybody has run into this and what may be the problem....can they get rootbound in 10 days?

temps look a little high and you need to lower you ph to about 6. and make sure that you are not overwatering poke holes in the cup so excess water can drain out.

Might be the light is too close..

I am having the same problems... I am quite new to all this but I had a fan failure.

how often are you watering ??

I just noticed the same problem on my small seedlings. We should compare to see which thing fixes it. My temps have been a little high (75-80), My ph is good, my lights were a little close.