Your roots look great honestly. But the plant is pretty small for being a month old. Also see the nutrient issue on the old lower growth. Perhaps raise your ppms. Go up to 400-500. That rockwool also looks pretty dry for my liking. I would top feed it more. Its to the point where it wont hurt it if its saturated. The roots all compact like that and with those microfishbones is a good thing.
What is your water temps when the lights are off? Id say it just took you a while to get the roots clean and those deffeciencies are from before. As to the stress it shows, also prolly from the uptake issue. I mean you have only had this lined out for like a week or so right? Give us some closeups on the top down of the plant. Id like to see what the new growth looks like, im sure it will be fine. Also you prolly just need to turn the light up a little bit now that shes established roots. I mentioned the water temps at night because they tend to drop. You want to stay around 72f at this pace since your roots are fine. If your res temps are dropping in the 60s when the lights are off that will also slow down your growth. All there is now is keeping it well fed, and making sure it gets enough light. I had you turn it down before cause it was amplifying your issues. Now we can test it again to see if thats why its so small still. . im sure thats all it is. Just remember, if you get more issues on older growth, that you need to back it back off and we will have to figure out what its not uptaking. Atm, id say you need another week of running good to say that its stunted.