I hate when people say "Soil" when they don't have a living soil with microbes. If you are using hydro nutrients with coco or peat or something just call it medium and not soil. As mentioned earlier, the chances of your nutrients being short something is rare. pH is going to be the culprit 99% of the time. And don't go flushing the shit out of a plant to try to fix the problem when again 99% of the time it's pH.