That’s your main problem. Your medium isn’t normal soil. It requires a much low PH value for the roots to absorb the nutrients. It get’s some of them, but not others. The ones it doesn’t absorb remain and build up as salt. At some point your roots stop absorbing anything (locked). You need to flush (reset) and PH at 5.8 with full nutes on your final watering. Do you know how to flush?After