Perhaps a zinc or iron deficiency, which may be due to a too high pH value in the substrate or in the water. This means that nutrients and trace elements are not available, which leads to deficiency symptoms. On the young yellow leaves iron on older leaves magnesium for example Would test the pH of the drain and regulate the water down to pH 5.8-6.2. As an idea. Wish you continued good growing💚✌️🍀