It really depends on the size and type of fish. Butterflies and tangs, for instance, like to eat multiple smaller meals throughout the day so we feed them with an auto feeder in the morning and frozen food in the evening. Most larger saltwater fish can do well on a single meal of quality frozen food daily though. On average, we would feed a fully stocked 600 gallon saltwater tank around 6-9 cubes of frozen food per day.