Really stupid question about sphag N bag

[nidiasophia]

Hi guys,

My name is Shelly, im new to the forums!

I have two questions about sphag n bag

1)I am trying to save a phalaenopsis wiht no roots using the sphag n bag technique. I heard superthrive is really good for this technique. I have a really stupid question though - I think I already know the answer but I need to be sure. After adding some superthrive to water, do you need to soak only the bottom part of the plant where the roots will grow for an hour? Not the entire plant, just the bottom right?

2)Right now I have had my plant sphag n bagged for about a week. There are three leaves left. I am noticing that the middle leaf is starting to turn yellow starting in the middle of the leaf, toward the base of the leaf. Why is this happening and how can I stop it?