Seedling leaves curling

Just checked up on my seedlings and noticed the cotyledon leaves curling? What would cause this or is this just a normal thing?

Seems to wet. I just changed to rapid rooters myself, so just figuring those out, but so far it's better than the rock wool.

Those cot leaves have just about served their purpose so I wouldn't worry about the curl. Pay attention to your newer leaves.

normal, relax

Ok, there looking good, was just wondering.