As a general rule of thumb, you should feed your koi and goldfish once per day, no more than they can eat in 5 minutes. If there is still uneaten food left after 5 minutes, try feeding less next time.
The amount of food required by koi and goldfish will vary widely depending on the season and temperature of the water. During the spring and summer, when the water is warm and the fish are very active, they will need more food. In the cold winter water, koi can go weeks without eating.