Roots turning brown when entering leca

[Ale_V]

Good morning everyone,

I have had a Cattleya in S/H for months (repotted after it finished blooming), but I feel like something is not quite right.

The roots seem to be growing properly (outside the pot), but the few that have made their way into the LECA substrate don't seem to be doing well: some appear to be dying, with their tips turning black, while others continue to grow but not in an ideal way.

On the other hand, the aerial roots seem to be thriving. I’d say that in the four months it has been in S/H, aside from the roots, the plant hasn’t grown a single millimeter.

I water once a week with 1/4 of the recommended dose of Rain Mix in RO water.
Temperature: 25°C during the day, 21°C at night.
Humidity: between 90% and 80%.

Thanks a lot for any advice!


Ale

PS: I've taken the plant to the window to take some pictures but it lives inside a greenhouse with artificial light.