brand new dendrobium with yellowing leaves

[maranta]

hello!
i'm a complete beginner to orchid growing, i have many other plants, but have always avoided orchids up until now. a few days ago i got my first, a dendrobium hollywood (i think) and its already getting yellow leaves! i want to try to save it before i lose that lovely inflorescence.

i have it in an east facing window, med to bright (no direct) light, and in the few days i've had it i've watered lightly once. and i checked its roots, which look healthy. its in bark, not sphagnum moss, maybe that's the problem?

thanks!