Never heard of bone meal for orchids. Did someone recommend it? I use the MSU fertilizers for orchids.
So sorry the house sitter did so horribly! Worst nightmare of mine! Yellow leaves can mean many things as you learned from the Oncidium! In other plants they are begging for water but it also can mean that the roots are rotting. How much watering did you give it? It may have been in trouble before you tried to save it.
