Goldfish usually do best when fed two or three times per day. At each feeding, it is best to put a small amount of food in the tank. If the goldfish eats all the food within one or two minutes, a second helping of similar size can be given.
Overfeeding is usually a bigger problem for goldfish than underfeeding, as goldfish can easily go two weeks or more without eating, especially if they are living in relatively cold water. Overfeeding can harm the fish directly by causing intestinal blockage and problems with the swim bladder. Overfeeding can also cause indirect harm by clogging the aquarium filter and polluting the water with rotting food.