Propagation: Has anyone used these "sponges"? I have a problem..., 1 by mominem

mominem wrote:
I bought these spongelike plugs on ebay, they are approx 1.5 inches tall and an inch square which is tapered at the tip. Very spongy but supposedly made of "composted organic materials" such as peat and bark, bound with some kind of polymer. Seeds germinate very readily in them and the roots travel through them very very easily & quickly. So it sounds all good, right? .... .... ...
Well, a few plants seem to sprout and remain yellow - such as tomatoes, parsley and par-cel (herb), brugmansia (but not datura). I planted the yellows in soil... now the new tomato leaves are green but the brugs are still yellow. I misted with kelp water and watered in a weak fertilizer but no change. Could it be the pH? or something else?

Any help is appreciated - I really like the way these sponges work but if the plant won't be healthy, it's not gonna fly.
Eileen