Stressed lady

dark green leaves is nitrogen excess, the rust spots are calcium deficiency. Cut back the NPK , only feed every third watering : two times plain water one time nutrients, that means NPK once every ten days minimum ! for cal mag you have a deficiency so you can add it every watering for one week then as a regular schedule. If you do this the problem will stop spreading almost immediately and the plant will be completely recovered in 10 days. Hope this helps ! 🚀