Is this an early warning of something wrong?

Hi guys,

Seeing the leaves in one of my plants flowers becoming quite yellow.

Week 3-4 of flower
Just added flower nutes 2 days ago
Ec is 1.52
Ph6.0

My green crack is the one that doesn't look so happy... Please let me know your thoughts?

I moved up from ec 1.4 to 1.5 and the pH from 5.8 to 6 in the last change out 2 days ago. My concern is nite lockout...

We'll probably flush it, and then come back with lower ec. Rockwool salt build up quick unless you doing runoff every watering. What is runoff ph n ec?