Dendrobium smillieae yellow spots on new growth

[jrengen]

I don't see any sap on the leaves. Checked already for insects, couldn't see anything. It's getting good water, light and food. I'm using MSU fertilizer weakly weekly. I thought it could need more magnesium, but don't know. The rest of the plant seems ok, maybe a spot here and there, but nothing really obvious. I moved it down the bench where there is a little more airflow. It will be interesting to see what happens.