It's probably not mold that you were seeing.......

Is the sponge itself green? As in when it was new it was green?

Does the sponge hang upside down in your humi? If so, the green "felt" type sponge has left a residue on the screen that holds it in.

I would get rid of the sponge and shot glass and either pick up a Paradigm system or use some beads from Heartfelt.......IMHO.