As a general rule, according to RSPCA, only feed a goldfish an amount that could be easily consumed in two minutes or less. The recommended amount is similar to the size of the goldfish's eye.
It is very crucial to avoid overfeeding goldfish as this can cause indigestion and potentially cause the tank or bowl to become contaminated. RSPCA recommends using small floating pellets, as they allow for easy removal of excess food. The smaller pellets also ensure that all fish in a tank aree getting a proper amount of food. Goldfish should usually be fed two to three times per day.