Can you submerge it in a way so that it is just below the surface? That may provide enough surface area for the newts to climb out.
You could also just keep scrubbing off the mold as it grows until there is no more growth, but there is no saying how long that could go on.
You could also acquire a new land area. An upside down flower pot, a large rock, a piece of corkbark or floating plants like anacharis or hornwort all make excellent land areas. All of these should be quite easy to find and cheap.