Yellow Shrivelling Pseudobulbs on Oncidium

[Mercurius]

I inherited this Oncidium from work (nobody else was capable of caring for it) and it's been having some issues. Some of the older bulbs are yellowing and getting all shrively and losing their leaves. I thought at first that it was just the older bulbs dying off, but the one at the far left of the pic had a new bulb starting that just also turned yellow. I typically soak it weekly with dilute fertiliser unless it seems too wet/dry, then I adjust accordingly. It used to sit on the kitchen counter with my phals and get the evening sun, but a few weeks ago I moved it to an east window with some other phals.