The closeup photo with the spots looks like a
Calcium deficiency. That could be caused by the pH being too high or too low (5.5-6.5 is ideal in hydro) or it might mean your tap water/nutrient system doesn't have enough Calcium and you may need a plant
Cal-Mag supplement (since you're using Advanced Nutrients, their Cal-Mag supplement is called
Sensi Cal-Mag Xtra). Needing extra Cal-Mag is relatively common in hydro and coco. Cannabis plants seem to love Calcium.
Also, what do the roots look like for your hydro plants? Are they bone white or do they have spots or patches of brown?
I noticed your coco-grown plant seems to be struggling a little. It looks dry and I wonder if it might need to be watered a little more often? It looks like it could bounce right back with a little TLC.
Overall your DWC plants look good. They don't look nutrient starved, though if you're still using seedling nutrients I'd definitely go to adult-strength vegetative nutrients by now. Like everyone said, your PPMs seem too low for the stage your plants are at. If the plants start getting pale or lime green all over (even though the pH is right and roots look good), that's another sign they need higher levels of nutrients overall.
Just curious, what grow lights are you using and how far are you keeping them from the tops of your plants?
You have a nice little garden developing!