I never use any humidifiers to keep my pipe tobacco moist because IMO with pipe tobacco it is better to have it too dry than too moist. I have never had any mold problems storing my tobacco this way.
Pipe tobacco is easily re-hydrated and if it does get a little dry, I spread it out on a paper plate and lightly spritz it with a spray bottle that has Distilled water in it. I then seal it up for a day or two to let the tobacco absorb the moisture and it's good to go.
I would rather re-hydrate my tobacco than lose it to mold.
P.S. I would also just throw out the humi disc as well. Better not to risk starting mold growth again.