In article , sophie-
says...
I started off in a similar situation to Tispe and now have a four foot
tank. Still wondering what to put in the little one; I fancy a) corys
and b) kuhlis. hrrrrrmmmmm.
fishkeeping is disturbingly addictive.

My advice: "borrow" one of your goldfish temporarily, set up the
old small tank, let it cycle, then leave it running and empty.
Sooner or later, you'll be wanting a hospital or isolation tank,
and an already-cycled one is a nice thing to have.