I think you are using pre-ferted soil. Those nute levels look okay but the plants tell a different story! I would flush, or better yet, start fresh with a different soil meant for seedlings. Try running a couple bagseeds to 3 or 4 nodes to test your setup before using good seeds. As for overwatering, that might be a problem too.
How are you adjusting the pH of your water? Where does teh water come from? Have you tried just running plain unadjusted tap water? That looks like burn. I wonder if it's from your pH adjustment, the soil, or something (sodium possibly) in your water? Very odd, because 'on paper' you should be fine with those specs!