Good deal for the measurements. Just wanted to make sure you weren't doing 1/4 of the recommend nute mix - that would be too lite prolly.
I figured that those roots belonged to the BFF - that is why I asked - She is not healthy and is not going to be until something changes, not sure what but something. If it is stunted, and droopy with roots like that, something is wrong. With the nice roots you had focused in the picture in mind you are obviously doing what you need to for the others to be healthy - that one is not. Any thing you can think of; damage, previous owner's neglect, bugs, diff amount of water from sprayers, could be a lot.