Cuttings in water have many problems... for that reason I only propagate in well drained soil. In this case I would apply 0,1% IBA (Rooting hormone) & keep soil damp not wet.
after the plantlets have formed I would seporate & place in potting soil then i would start dilute fertilizer treatments. the fertilizer will be primarly for plant growth & 3rd concern would be to further promote root growth

Thanks for your reply.

For some reason, African Violets tend not to respond well to rooting hormone; in my experiments they spend a lot longer making roots and forget to propagate, but the chances of rooting are no higher. Given you can get just as strong of plants in less time, many people choose to not use hormones.

I wasn't suggesting not using soil, sorry if it sounded that way. Rather I meant tat I was only "feeding" the leaf with water, not fertilized water. I'm curious as to how the fertilizer effects the leaf and why.