Agreed. This set up would not be ideal for goldfish. However, if this is a 20 long and if you add a heater it would work great for a few african shell dwellers (cichlids). You could still do a really cool tank this way.
With fish, it is sometimes easier to look at what you have for a set up first and then find the fish to go with it. There is always going to be something out there that should work for you. Maybe even something that you will like more than goldfish.