I recently germinated and planted six vigna caracalla seeds, and they all did well for a few weeks.Then one of the seedlings' leaves began to yellow slowly, and after a few days it curled up dead and now the other seedlings are beginning to go the same way.

I have noticed a hard crumbly white substance forming on the top of the soil and on some of the leaves, as well as some little tiny bugs flying around my plants. I am growing thunbergia alata in containers next to the vigna caracalla, with the same white stuff and little bugs, but they seem to be very, very happy.

All the plants are were started from seed and are currently inside in front of a large window. They are watered every few days, most often with straight water but every now and again with a light miracle-gro mix or with an epsom-salt mix.

is the white stuff a mold or fungus that might be killing my snail vines, or is it the little bugs, or is it something else entirely?

I really want them to live, but I don't know what to do. Any thoughts or suggestions would be very much appreciated! Thanks!!