I couldn't solve the problem, help

if it started at the bottom, N-deficiency. otherwise there are a few trace elements that can pale like that... but that would more likely be a pH or lockout issue as trace elements are usually in soil or included with any soilless/hydro nutrient lineup. boron tox, manganese deficiency, zinc deficiency, iron deficiency ... this stuff is not 1:1 discrete. there are multiple causes for most symptoms that are possible. progression and where it starts can help eliminate some of them... along with knowing how much you feed (not jsut overall concentration buy per molecule of need), you can usually have a well-educated guess. the better your soilless/hydro formula is or soil fertilization is, the easier it is to diagnose and the more patient you can be to identify a slow-progressign issue. Keep refining.. issues become easier until you very rarely encounter them.