Slow Seedling Growth with Yellowing New Leaves

Hey folks, could use an experienced eye on my DWC seedling which is 16 days old. She has barely started to grow the second set of true leaves, roots haven't made its away out of the netpot, and I've been top watering with RO water everyday on a 18/6 schedule under a HLG65 @ 2ft. New growth is somewhere between yellow and lime green and the growth has been excruciatingly slow.

I understand we should not start 1/4 nutes until atleast 3-4 sets of true leaves have developed and roots have hit the water. But since one of the cotyledons have shrunk, I was assuming this stunted growth is atleast partly attributed to exhausted nute reserves. Should I start with 1/8th - 1/4th nutes in the res, or should I just keep waiting until the roots drop or the second set of true leaves mature. Not sure if there is any other issue at play here, hopefully the pics would help.