Save Orchid with no leave but a keiki

[JanetL]

I have this Phalaenopsis orchid for 6 months. After flowering it had grown 3 new leaves, some new roots and a keiki right below the dried flowers. A month a ago I saw a black spot on the side of its crown despite that I've being carefully watering it to avoid crown rot. It still happened IF it's the case. And then the leaves start to turn yellow one by one from the bottom. Now it has only one little leaf and the keiki left. And the leaf is loose, so I'm afraid that it is falling off soon.

Anybody know how to save a orchid like this? I heard about using hydrogen peroxide to spray the crown area to treat crown rot. But this is my first orchid, so I'm not sure if this is a case of crown rot.