When tanking down, be sure the water pumped into the fish hold is full-strength seawater. Take water from the middle of a sound, away from glacier and river runoff, if possible. If you must tank down in harbor, do so towards the peak of the flood. Seawater that is diluted with fresh water will freeze up the chiller before desired hold temperature is reached. Adding freshwater ice to the fish hold before tanking down, to “jump start” the system (so the system doesn't have to be run on the way out to the grounds) reduces the salinity of the water and raises its freezing temperature, making freezing-up more of a concern. Starting with ice is OK for chilling round salmon, where we're trying for an optimum temperature that ensures consistent product quality (we don't want to freeze eggs), but not for, for example, blackcod, where we are trying for the lowest possible temperature without freezing up the chiller.