Dendrobium dark spot leaf
 

Dendrobium Ekolu x Little Atro-
got it in 1/2020, then started noticing the dark spots on leaves, and leaf will fall off.

I removed all the media, and has just been watering the roots and let air dry regularly (without any media). I see that there are new roots and new canes growing.

Few months after no media, I'm still seeing new dark spots on leaf. Are the older roots dead? Do I need to completely remove them? What temperature range do they like?

Attached photos from Jan and now.

Any suggestions?

This is in the Latouria group of Dendrobiums. They prefer to be evenly moist all year. The pseudobulbs are very wrinkled from drying out too much.

When they don't get enough water, their leaves look awful. I would suspect that. Fungal diseases are much less likely. The oldest leaves, on the smallest pseudobulbs, are the ones dropping off.

Most of the time Dendrobiums make new roots only as they begin new growth. The time to repot is when the new roots are very short nubs. You are a little past that stage, but this plant isn't happy bare root. Pot it now into any medium you like. Use a pot that just holds the existing roots. Do your best not to damage existing roots. It is not necessary to cram the medium tightly into the pot. You may need to stake the plant to hold it upright until it grows new roots.

It is important this type of Den stays moist, but still has plenty of air at the roots. Also, they are not extremely high light plants. Bright shade is generally good enough for them to flower.