Possible calcium def or ph issue?

[Cannaleaf9]

I need some help identifying this issue. Fox farm OF and HF mix. Full spectrum LED with light at 24" at 30% power. RO water. temp 77. RH 60-65. Runoff was at 6.0 ph.

One of my plants have been showing this issue for the past week. Here are pictures of the progression from day to day. Day 11 after sprout at the moment. I have not given any nutrients yet which is why i'm thinking on day 11 it could be a calcium deficiency especially with a ph at 6.0. Thoughts??

 

[jguit]

The newest set of leaves coming out look pretty good. I'd grow it out a bit and see. Could just be a fluke. I've had seedlings do all sorts of weird shit! I doubt it's a deficiency at this point.