Burnt tips and edges on leaves can often indicate nutrient burn or toxicity. This could be caused by overfeeding or incorrect nutrient ratios in your feeding regimen. However, if you're using a super soil medium, nutrient burn is less likely unless you've added additional nutrients that the soil couldn't handle.
Dark-brown discoloration on the leaves could be a sign of various issues, including nutrient deficiencies, nutrient lockout, or even pest or disease issues. Without more specific details about the appearance and distribution of the discoloration, it's hard to determine the exact cause.
The brown rust-like patches on one leaf could potentially be a sign of a fungal infection like septoria. Septoria typically presents as small, circular brown spots with a lighter center and can spread rapidly if not addressed promptly.
Considering your setup and symptoms, it's possible that you might be dealing with a calcium or magnesium deficiency, which could lead to burnt tips and edges and discoloration. However, without a closer examination or additional information about your feeding schedule and water pH, it's challenging to confirm.
I'd recommend closely inspecting your plants for any signs of pests or diseases, checking the pH of your water and soil, and adjusting your feeding regimen if necessary. If the issue persists or worsens, you may need to consult with experienced growers or a plant health specialist to identify and address the problem accurately.