| The white growth is probably a fungal growth but while I have seen it fairly regularly it does not seem to attack the orchid. I usually remove and replace all the medium and forget about it.
Your little Dendrobium keiki looks like a Nobile Den. You will know when it flowers (Jan-March in the northern hemisphere probably June-Aug for you) because the flowers on a Nobile grow from the cane not on a stem like common Den. With either type Den you do not need to do anything special. If you are growing them outside give them as much light as they will take without the leaves browning.
The second photo of the dead leaf is more important. The blackening at the bottom of the leaf is a sign of fungal infection. If you see this type of blackening on a green leaf it is serious and can destroy a plant rapidly. Since your photo is of a yellow leaf it may be aftermath of a leaf dying of old age and not a serious problem. When it is fungal the rot will spread rapidly and needs to be cut off before it reaches the rhizome.
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jerry  |