Brown dark spots on fan leaf

Hi @Green_Dream At the beginning of the calcium deficiency, the leaves also turn dark green but a darker green more pale. I am also more inclined towards Phosphorus deficiency due to the appearance of the leaves, but if more black spots like this appear on the leaves, it will probably be a calcium deficiency, if you already feed it with calcium and it doesn’t effect it can also be the accumulation of mineral salts in the substrate, preventing the roots from feeding on calcium and mg, you will have to make a flush and only then apply calcium and mg. good luck mate 👍