DWC seedlings HELP!

So I'm on Day 7 of my first time growing using DWC method. Everything seems to being going OK except I feel like she's growing a little slower than the norm and the first two fan leaves seem to be curling downward on the ends. I've read that this could be N-tox, too much lighting, and numerous others. My setup is 2x2x4 with a 200cfm exhaust fan leading to an external carbon filter, 300 watt LED panel which puts out roughly 140 watts I think, I have a 5 gallon bubbler bucket with hydroton, and started germination in a rockwool cube and have since put the cube in the hydroton. I keep the pH between 5.5 and 6.0 exactly, the humidity I keep between 50%-65% and temperature fluctuates between 68° to 79° from night to day. Today I removed the rockwool to check root growth on the bottom and it is growing straight down toward the res like I want but I'm seeing very slow growth on the top and the curved fan leaves. Any ideas what this could be? Anything I should change? This is my first time so I've tried to pay close attention to everything and do it the right way. Oh and I have yet to feed nutes because I've read you should wait until 2-3 weeks and the water I'm using is out of the tap which I let sit 24 hours to get rid of chlorine. Any advice would be great!

 

Awesome, that's good im glad to hear it! These leaves curling down have had me nervous the past few days. I have put a lot of time and effort into this and I want it to be perfect! Thanks for the quick response!