P deficiency canna coco

hey there Draxel, the good news is you have a fully healthy plant no deficiencies. this you can see because there are no signs of stress like red stems and roots and other issues like the problem is spreading. Looks like just one leaf right? so it's probably something that happened during watering, some contact with the water or something, maybe it's just natural dying of the lowest and oldest leafs . About your runoff, that's also totally perfect. the difference between input and output is the absorption by the plant (more or less) . So it's a good thing, and a good sign that your plant is eating and growing well. the worst thing you can do is to panic, flush or over feed. just follow your original plan and take the leaf off when it's fully dead, it's no problem. Hope this helps ! 🚀