FWIW I add 20 drops of Guliard F/2 (aka. FAF's Micro Algae Grow) to 2 L of saltwater before sterilizing. That's enough media to grow the culture to the max, at which point you harvest 50-75% and then refill the culture vessel with fertilized/sterilized water again. In other words, I do not fertilize the cultures while they're just sitting there (and you shouldn't have to). Running a total of 4 species, 6 Liters (3 2 Liter Bottles) per species, I produce roughly 3 gallons of phytoplankton per week.
MP