Welcome!
I use s/h for my cattleyas with great success.
I personally have not had good success using s/h for my oncidiums. I use Aussie Gold for them which I don't know alot of people that use this.
Good luck with it though
The dendrobiums I don't grow but my hubby has a few. He was willing to let them out until the weather was 40's but I went out and brought them in
We are arguing over it a bit still
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They do need to get cold though.
Soft water is probably more of an issue with your Oncidiums than humidity. Try distilled water from the super market and fertilize sparingly.