Center of seedlings turning yellow


First DWC grow Amnesia Auto, center of seedlings are turning yellow looking for any help
Started from seed in rockwool 11/3
6.5 inch baskets expanded clay in 5gl buckets with 2.5gl of distilled water
Yellow on tips of leaves on 11/15
Started 1/4 nutrients 11/17 yellowing moved to center of leaves
PPM 350
Using a MarsHydro 2000w 25%
Still yellow 11/22 root growth seems to be good

It’s normal. Chlorophyll will step in and do its thing in several days.