You'll find two photos below.
The first photo is of a plant that isn't doing too well, and is clearly wilting (though still hanging in there) despite being in a similar state for almost two weeks now.
The second photo is of a more recently "moved" from soil sapling to the hydroponics system that although it isn't doing too well, at least is showing signs of some new leaves appearing. Though it is leaning quite a bit (looks like it's towards a secondary source of indirect light coming through the windows; though it isn't particularly strong).
Now, it is very possible that the cause of this is nutrient imbalance, I don't have a good grasp on nutrient balance, but in the past, I've managed to grow some fairly large plum tomato plants on the same nutrient mix, so I'm hesitant with just assuming that this is the issue.
The thing that is very different from that point is the fact that I'm using indoor growing lights right now, and it's possible that it's simply not enough light exposure? I'm not sure if there are any particular signs I should look out for that would indicate this? It's a 40W led lamp situated roughly 0.5m (20 inches) above the actual hydroponics "rig".
What do you guys think? I'm obviously doing something wrong.