To solve the issue you can reroute it to a vent which is going out of your attic.
White growing chimney attic.
The moisture picks up minerals carries them to the surface of the masonry and leaves them behind in the form of tiny crystals on the surface as the moisture evaporates.
The best way for getting rid of mold in the attic black mold and any other mold is to remove it from the surface it s growing on or remove the contaminated surface.
The stains tell us that water has been entering the flue raising an alert for frost damage.
Efflorescence occurs when moisture moves through concrete or other masonry.
This is not just a cosmetic concern.
Flue gases and sparks can enter the building.
And the rh from the grow tent air is very likely to get stuck with this heat and cause mold on the attic.
What is that white stuff on my chimney.
It is important to notice stains on a chimney exterior surface.
Stains from water creosote or soot leaking out of a chimney such as in this attic.