It's probably like the Sub Tank Mini's, a bit difficult to get off the first time. Being glass it won't screw off, not having threads and all. If it is like the STm's, and from the looks of it it might be, then you have to twist and pull, eventually it will come off. Sometimes I had to get my fingernail between the edge of the glass and the metal frame and help it separate. Don't use anything rigid like a screwdriver, it will likely crack the glass.