I bought a goldfish bowl kit at the York show earlier this year. It has been a job-to-be-done-soon in my craftbox until this morning.
The rubbery scenic water melts within a few minutes of dropping the tube in a cup of hot water. I poured a little in the bowl to make an invisible base for the fish, added the greens, then topped it up once the base had set.
I'm not sure of the scale: he looks a little cramped in his bowl. Poor fish!