K deficiency?

Looking at the image you shared, it appears that your plants are experiencing a condition known as septoria leaf spot. Septoria leaf spot is a common fungal disease that affects many plants, including cannabis. It is characterized by the appearance of brown spots or necrosis on the leaves, accompanied by a yellow halo around the spots. To address this issue, I would recommend taking the following measures: Remove affected leaves: If the leaves show symptoms of septoria leaf spot, it is important to remove them immediately to prevent the spread of the disease. Make sure to properly dispose of the diseased leaves, away from your healthy plants. Improve air circulation: Septoria leaf spot tends to spread in humid environments with poor air circulation. Ensure good ventilation in your growing space by using fans to keep the air moving and reduce humidity. Adjust humidity levels: Reducing humidity can help prevent the development and spread of fungal diseases. Make sure to maintain appropriate humidity levels in your grow tent, avoiding excess moisture that promotes fungal growth. Consider fungicidal treatments: If the disease persists despite your preventive efforts, you may consider using specific fungicidal treatments for controlling septoria leaf spot. Consult with a cannabis cultivation specialist for recommendations on suitable products and their safe application. Remember, prevention and early management of diseases are crucial for maintaining healthy plants and maximizing production. I hope this information is helpful to you, and I wish you good luck in managing septoria leaf spot and your future cultivation endeavors.