Disease or Deficiency? Or something else?

It's challenging to diagnose plant issues with absolute certainty without seeing the plant and its growing conditions in person, but I can certainly provide some insights based on the information you've provided. It appears that your plant is experiencing multiple issues, and it's possible that they are interconnected. Let's break down the potential problems: Red Spots Appearing from Bottom Up: Red or purple spots on cannabis leaves can be a sign of phosphorus deficiency, especially when they start at the bottom of the plant and progress upwards. Phosphorus is important for flowering and overall plant health. Previous Nutrient Lockout: If you've experienced nutrient lockout due to underwatering and silica buildup, it could have damaged the root system, making it difficult for the plant to absorb nutrients effectively. This can contribute to nutrient deficiencies and other problems. Burnt Edges on Top Leaves: Burnt edges on the top leaves are often a sign of nutrient excess or nutrient burn. It's possible that by adding CalMag, you may have overcompensated for previous nutrient issues. Leaves Coming Off: If leaves are falling off your plant, it could be a result of multiple factors, including stress from nutrient issues, pest infestations, or other environmental stressors. Runoff pH: A pH of 6.9 in the runoff may be too high for optimal nutrient uptake by your cannabis plant. Cannabis generally prefers a pH range of 6.0 to 6.5 for soil growing. A pH that's too high or too low can affect nutrient availability. Leaf Septoria: Leaf septoria is a fungal disease that typically manifests as small, brown spots with yellow halos. It's a separate issue from nutrient problems and may require specific treatments like fungicides. Given the combination of problems you've described, it's essential to address them step by step: Check your watering practices to ensure you're maintaining consistent moisture levels without overwatering or underwatering. Adjust your nutrient regimen to avoid overfeeding, especially if you've recently added CalMag. A balanced, complete nutrient regimen is essential for cannabis growth. Monitor and control the pH of your watering solution to ensure it falls within the optimal range for soil or your growing medium. Consider addressing the possible phosphorus deficiency with a phosphorus-rich fertilizer. If you suspect leaf septoria, consider using appropriate fungicides or treatments to combat the fungal infection. It's advisable to closely monitor your plant's progress, make gradual changes, and be patient. Cannabis plants can recover from various issues if you provide the right care and adjustments. If the problems persist or worsen, you may want to consult with experienced cannabis growers or a professional in the field to provide on-site assistance and guidance.