dendrobium leaf discoloration (yellowing, spots, dropped leaves)

[lithops]

I'm somewhat new to the orchid hobby, and after a good number of phal rescues I branched out and bought my first dendrobium a few weeks ago.

Pretty blooms, a few baby canes; I thought I'd chosen a healthy plant until a few days passed and the blooms on the third spike started to pale and develop softer brown spots on them.