Possible problem - rusty powder - with Dendrobium Tetragonum in orchid/plant case?

[daemondamian]

Hi folks,
I apologize for this long post but I'm not sure if I have a problem with my Dendrobium tetragonum mounted in my orchid case and wanted to offer as many details as possible.

Short version: I have Dendrobium tetragonum in my orchid case which might have a problem and I'm not sure what to do about it - what do you think based on the photos/description?

Long version:

Since putting it in there (maybe 4 or more months ago) it lost two leaves (possible due to old age?) but grewn a new cane with leaves and flowered from the new cane and 2 older canes.

The reason why I suspect a problem is there is an orange rusty looking 'powder' on the leaves and canes which doesn't come off after being sprayed with water (I haven't tried to rub it off as it's too difficult to do so in it's location).

I've added a few photos that show the plant- it looks more orange/rusty to the eye but the flash washed it out.

There is some black spot fungus on one of the leaves due to readjustments made to the humidity/fans and from one time accidentally leaving the fans off over night when I turned them off to take photos )

It has had that 'powder' for some months now.

Orchid case specs:
92cm long by 46cm wide by about almost 160cm tall. Constructed with 6mm perspex except the bottom which is glass (old aquarium).

It's maybe about 10cm from the top under 120 watts of 10000K(? cool daylight) tube fluorescent lighting (there's an additional 100 or so watts of compact fluorescent on the sides as well- the compacts used to be on top but were too high in the hood I made so it wasn't that bright to begin until I swapped around the lights)

Currently gets misted with pure RO water once in the morning (actually have it on for 5 whole minutes but it still doesn't completely water everything(!) so I hand water 1-3 times a week with tap water with seaweed and fish ferts or occasionally with a tiny bit of powder orchid fertilizer added).

I was allowing a day or so to dry out in winter/colder weather but am thinking of adding a few seconds through out the day to increase humidity and drop temps on very hot days (Summer here in Australia).

It was sprayed a few times with a natural garlic chili pest spray and pyrethrum, eco oil, neem oil spray.

Temps have ranged from 10 to 25c+ depending on weather and whether or not the heating or airconditioner has been on in the room; there's a 7 watt heat cord laid out in the bottom as well as a 100W aquarium heater in the water section that are on a thermostat to turn on if the temperature drops below 15c or off if it goes above.

Fans (2 x 12cm at the top) go continuously (except when mister is on) - they produce a gentle breeze which does dry things out before lights out (except some of the background - capillary matting on compressed cork board - stays moist/wet lower down) - here's