Keep stretching that cock, because that's not the worst thing that you can see in hydro... The leaves closest to the media don't always look all that purdy...
You're getting ready to crank up your nute strength, no? Were those clones or seed?
Pics of whole plant are helpful. How's the newer growth?

You've got some really important data missing in the troubleshoot form... check your res temp, and monitor the res pH. That doesn't look like an issue though. Res temp may be a bit high... ?