the dark wax is just a sign of "constipation"...which basically only means, whatever is waste/not wanted is not going down and out fast enough. (open-channeled enough) So it goes 'up and out'. Or, it's too concentrated, lacking hydration. Or both. and so on...
'down and out', 'up and up'...
hmm.. makes a person think about some of the posts we see around here, don'it?