Just to add: 1 inch of full grown Goldfish per 2.5 gallons. Keeping them in small tanks can promote growth stunting which is where the outside of the fish stops growing and the inside keeps growing. This is where most people think that fish grow to the size of their tanks. It is very painful for the fish and a nasty way for them to die. I am not trying to be rude or bash you I am just informing you