Sorry just saw u have sec
Yellow leaves can be a sign of a few things, but in deep water culture, it's often related to nutrient problems. It could be a deficiency, meaning the plant isn't getting enough of something it needs, or it could be a toxicity, meaning there's too much of something. Sometimes pH imbalances can also cause yellowing because the plant can't absorb nutrients properly when the pH is off.
Do you know if you're using the right nutrient solution and keeping an eye on the pH?
In dwc it’s probably not calcium toxicity because cal toxicity in dec looks like
Calcium toxicity in cannabis plants can show up in a few ways. You might see the leaves turning a darker green, sometimes with a purplish or brownish tint. They can also get thick and leathery, and you might notice some curling or twisting. It's also possible to see yellowing between the veins of the leaves, while the veins themselves stay green.
To me in dwc it sounds like it could be sulfur toxicity. The yellowing starts in the center of the leaves and spreads outward, and the veins usually turn yellow or bronze or red. It's not super common, but it can happen if there's too much sulfur in the nutrient solution.
Good luck check if you’re starting to have root problems and getting the nasty looking roots that could be the problem. Always adding something like hydro hairs to your resivour can do wanders to keep a plant healthy and even keep nutrients in bal