this is very similar to the problem im experiencing, and im not going to make my own thread yet if i can find the problem someone else is experiencing...

Instead of foxfarm im using happy frog, they are 2-3 weeks old and are working in their 3rd node but its really slow(when comparing to other ppls pics my plants seem they should be on their 5-7node), the cotlydon is pretty much yellow with grey spots and the first node is beginning to get discoloration on the edges of the leaf while the entire leaf is yellow, one of my seedlings, is yellow w/ grey splotches, but the first node is folded down and its basically not growing.

i have some younger ones that are still working on their first node and are looking good as of still, but im worried... i dont know the PH of the water but its tap water. I dont know exact temps, or humidity... i dont have an intake fan but i do have a fan on the plants, i go in there every 8-16 hours so they get fresh air then... i assume they aren't big or old enough to need more fresh air yet, and i do plan on getting proper ventilation as time goes on and they get bigger.