Thanks heaps, catbuds!

I'm kind of thinking the same thing (but everything here *should* be clean). Solo cups are new, the coco mix is new (or at least previously unused). I expanded it from brick about 7 months ago and it's been stored in a trash bag since. It feels completely dry.

Used hydrogen peroxide the last round and it didn't change the outcome. But, I didn't spray the plants like Shov suggested. Started two more seeds Friday night and they're already in the coco. This will be the same as last round except I'll run the lights closer, adjust the ventilation and spray the plants. Solution remains the same (germination and seedling growth): 5:1 tap water / H2O2, pH adjusted to 5.8-6.0.

I think if this round fails, it will pretty much prove the damping theory. If that's it, I'll sterilize everything.

Thanks again -- it helps!