Nitrogen ?

A fungal problem caused by inadequate ventilation/too high a humidity level. Opening the other end (wall) will solve the problem. Your plants need good air flow-through and proper ventilation/air exchange. Having only vents near the bottom means the air at the top of your tunnel gets super heated and saturated with moisture, leading to fungal problems. The layer of perlite on the ground just compounds the problem, as it will hold moisture and add to the excess humidity you are experiencing. Removing it carefully would also help reduce your humidity problem. Hope this helps, Organoman.

Look like a potassium deficiency. Possibly zinc. I personally would lean towards potassium. Plus check your soil ph it might be getting close to out of a decent growing range. Good luck and happy growing

If it's on the lower leaves then it will be nitrogen deficiency, if it's not on the lowest set of leaves I would start by checking your pH and then make adjustments from there.