autoflower plant developed brown tips and edges then spreads inward

one of my plants is developing brown tips on middle-of-the-plant leaves, it starts on the tips and edges then moves toward the center of the leaves. No camera to post pics. New growth looks healthy. these are autoflowers. i have compared what mine look like to a nute deficiency chart photos but mine do not look like any of the examples. the leaves this is happening to are in the middle of the plant, so i know it isnt light burn. i planted these in a mixture of 5 parts peat moss, 3 parts pearlite, 2 parts worm castings, 4.5 cups of epsoma plant-tone fertilizer (5-3-3) per cubic foot. plants are approx 2-1/2 - 3 weeks old. all of my other plants look fine. no bugs. what do you think this is? thanks

May also be heat stress, especially if it's occurring on the tips of the plants. What are your temperatures like?
May be nitrogen toxicity (too much nitrogen), it turns the leaves brown and they eventually will fall off. Without pictures it's hard to say. Are the unaffected leaves dark green, because if so then it's defiantly over feeding.

temps 70-85 degrees. the plant only has 4 nodes, the 1st node with single blade leaves looks fine, as do the top node newest leaves. the second node leaves are the worst, the brownness having spread to the vein in some places, and parts of this leaf set are turning light green on theor way to brown. the 3rd node leaves just the tips and a few of the serrated edges are beginning to brown. Overall the rest of the plant and parts of the browning leaves that are still green are a good color, not overly green... the strange thing is i have 10 plants going and this is only happening to one plant, which is neither the tallest nor shortest of the bunch...

I should note that this situation came on suddenly, i watered 2 days ago and did not notice anything wrong with the plant.