Dendrobium Aberrans with white dried spots on leaves

[edisonghc]

Just purchased this last week from a local shop. I'm growing it in bright artificial light, temp from mid to high 70s day and night, humidity 50~70, constant airflow from a fan, water when media is dry about every 5 days, 50ppm water not fertilized yet, only a tiny bit of calmag, (.5 ml in a gal) once.

First 3 photos are taking in 3 consecutive days. I applied Physan on Day 2 but that didn’t seem to stop the spread. There is very subtle yellow marks around the dry white spots, more pronounced on the backside.

Any ideas on what may be causing this? Fungi/bacteria? Or light/water related issue? Appreciate any help!

Original posted on: Help identify the cause of leaf white spots on Dendrobium Aberrans : orchids