Thanks for the suggestion! I transplanted it into the bigger pot, so at least we can take that variable out of the equation. It definitely had a thick mass of roots! I will only leave them in the red cups for a week or 10 days going forward to see if this is the cure.
Plant is just over two weeks since sprouting and the lower leaves are turning yellow then brown and dying, very crispy. Using distilled water, Roots organic soil, no ferts other than what is in soil mix. Lights are T5, about 2 inches from top of plant. Suggestions?