Leaves turning yellow on newly potted Phal

[Orchid Whisperer]

Re: watering frequency, the OP had repotted to charcoal (from the photos, it appears to be quite coarse charcoal). Every 4 days might not be too bad, but it should be judged based on what the OP is seeing.

In that climate, it it were bark, it would be too often.

I recall a grower in Vietnam (on Orchidgeeks) that also had quite moist conditions but grew gigantic plants potted in charcoal. I don't recall his exact cultural practices though.