Sorry @Shuggz with the time difference, I was at work today and I can’t check the forum while I am working!
The pH in is ok in but the 5.9 runoff is telling us something else.
Tell me the brand name and name of the soil you are using and what the ingredients are from the bag, please @Shuggz
The stem color can be a number of things including genetics. I wouldn’t be concerned unless we see other issues.