New Grow Questions

Ok so I’m new to this but I have done a lot of research before starting. I’m my research I decided to go with an 8x8 grow tent and inside I currently have 2 Mars Hydro tsw2000(300 watt) and 1 MH tsl2000(300 watt) running over 6 plants. 3 fans in total circulating air a bag of exhale for CO2. My question relates to Ph and nutrients. I’m using coco and perlite and in a few trial pots I mixed in a small part of compost. My first planted plant I didn’t Low stress train until it was a bit late. The bottom fan leaves are turning yellow but after a flush they seem to be actually pigmenting back to a lighter shade of green. The whole plant looks healthy and the leaves are light green. However 2 of my plants seem to be experiencing the opposite end of the spectrum in regards to I believe Nitrogen toxicity. I use RO water and use Cal Mag and Fox Farms and General Hydroponics nutes. What does my ph need to be at? And what are these plants likely experiencing? Thoughts?

Ps I am coming up on the 6th week of veg. I run 2 additional lights in a separate area for my veg plants. These are about to be flipped to flower in the next few days.

In soil you want to be around 6.5 area. Different phenos feed different so back of the nitrogen some on the plant that is dark green. The other one looks rather healthy. That one leaf down the bottom is dying off as it dont get light and the plant has no use for it so its pulling the nutrients from it.

Scratch that....coco you want to Ph in that 5.8 area.