Hi orchid lovers, can anyone please tell me why my orchid roots are turning brown? The ones changing their colour are all exposed in the air by the way.

The same orchid in the pic below has lost two leaves since I have acquired a month ago but otherwise it has sent up two spikes and putting out a leave. It is potted in bark and I have been watering it every week. It's day six since the last time I watered. And by looking at the second photo, do you think I have to hold off the watering until the roots turns grey ?

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