Here’s the first problem. Mg seems like a no brainer, but usually ends up screwing you somewhere.
PH 6 isn’t terrible for a straight coco grow, this is more soil-y I think. For sure if your root zone pH (from a slurry test) is at 7.0-7.5 it’s far too high. Whether soil or non soil
Do you have current pics taken under normal light? Full plant and then some of the “yellow” leaves?
I went to your other thread, and tried to piece it all together. It’s usually best to start 1 thread, fill out a support ticket, and stay on that topic.
If you’re using RO water be sure to add extra calcium and magnesium